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[RFC PATCH v2 0/7] x86/idle: add halt poll support

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  [RFC PATCH v2 0/7] x86/idle: add halt poll support Yang Zhang <yang.zhang.wz@gmail.com> - 2017-08-29 13:50 +0200
    [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path Yang Zhang <yang.zhang.wz@gmail.com> - 2017-08-29 13:50 +0200
      Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle  path Peter Zijlstra <peterz@infradead.org> - 2017-08-29 14:50 +0200
        Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle  path Quan Xu <quan.xu0@gmail.com> - 2017-09-01 08:00 +0200
      Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle  path Borislav Petkov <bp@alien8.de> - 2017-08-29 16:40 +0200
        Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle  path Quan Xu <quan.xu0@gmail.com> - 2017-09-01 09:00 +0200
    [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops Yang Zhang <yang.zhang.wz@gmail.com> - 2017-08-29 13:50 +0200
      Re: [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2017-08-29 16:10 +0200
        Re: [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops Juergen Gross <jgross@suse.com> - 2017-08-30 09:40 +0200
        Re: [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops Yang Zhang <yang.zhang.wz@gmail.com> - 2017-09-01 09:00 +0200
    [RFC PATCH v2 5/7] Documentation: Add three sysctls for smart idle poll Yang Zhang <yang.zhang.wz@gmail.com> - 2017-08-29 13:50 +0200
      Re: [RFC PATCH v2 5/7] Documentation: Add three sysctls for smart  idle poll "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-08-29 19:30 +0200
    [RFC PATCH v2 2/7] KVM guest: register kvm_idle_poll for pv_idle_ops Yang Zhang <yang.zhang.wz@gmail.com> - 2017-08-29 13:50 +0200
    [RFC PATCH v2 4/7] x86/paravirt: Add update in x86/paravirt pv_idle_ops Yang Zhang <yang.zhang.wz@gmail.com> - 2017-08-29 13:50 +0200
    [RFC PATCH v2 7/7] sched/idle: update poll time when wakeup from idle Yang Zhang <yang.zhang.wz@gmail.com> - 2017-08-29 13:50 +0200
      Re: [RFC PATCH v2 7/7] sched/idle: update poll time when wakeup from  idle Peter Zijlstra <peterz@infradead.org> - 2017-08-29 14:50 +0200
        Re: [RFC PATCH v2 7/7] sched/idle: update poll time when wakeup from  idle Yang Zhang <yang.zhang.wz@gmail.com> - 2017-09-01 09:40 +0200
    Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support Alexander Graf <agraf@suse.de> - 2017-08-29 14:00 +0200
      Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support Yang Zhang <yang.zhang.wz@gmail.com> - 2017-09-01 08:30 +0200
    Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support Andi Kleen <andi@firstfloor.org> - 2017-08-29 15:10 +0200
    Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support Wanpeng Li <kernellwp@gmail.com> - 2017-08-29 16:10 +0200
      Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2017-08-29 16:30 +0200
      Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-29 16:40 +0200
      Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support Yang Zhang <yang.zhang.wz@gmail.com> - 2017-09-01 08:40 +0200
        Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support Wanpeng Li <kernellwp@gmail.com> - 2017-09-01 09:00 +0200
      Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support Yang Zhang <yang.zhang.wz@gmail.com> - 2017-09-01 08:50 +0200
        Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support Wanpeng Li <kernellwp@gmail.com> - 2017-09-01 09:00 +0200
          Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support Yang Zhang <yang.zhang.wz@gmail.com> - 2017-09-01 10:00 +0200
    Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-29 17:00 +0200

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#1722395 — [RFC PATCH v2 0/7] x86/idle: add halt poll support

Some latency-intensive workload will see obviously performance 
drop when running inside VM. The main reason is that the overhead 
is amplified when running inside VM. The most cost i have seen is 
inside idle path. 

This patch introduces a new mechanism to poll for a while before 
entering idle state. If schedule is needed during poll, then we 
don't need to goes through the heavy overhead path. 

Here is the data we get when running benchmark contextswitch to measure
the latency(lower is better):

   1. w/o patch:
      2493.14 ns/ctxsw -- 200.3 %CPU
   
   2. w/ patch:
      halt_poll_threshold=10000 -- 1485.96ns/ctxsw -- 201.0 %CPU
      halt_poll_threshold=20000 -- 1391.26 ns/ctxsw -- 200.7 %CPU
      halt_poll_threshold=30000 -- 1488.55 ns/ctxsw -- 200.1 %CPU
      halt_poll_threshold=500000 -- 1159.14 ns/ctxsw -- 201.5 %CPU
   
   3. kvm dynamic poll
      halt_poll_ns=10000 -- 2296.11 ns/ctxsw -- 201.2 %CPU
      halt_poll_ns=20000 -- 2599.7 ns/ctxsw -- 201.7 %CPU
      halt_poll_ns=30000 -- 2588.68 ns/ctxsw -- 211.6 %CPU
      halt_poll_ns=500000 -- 2423.20 ns/ctxsw -- 229.2 %CPU
   
   4. idle=poll
      2050.1 ns/ctxsw -- 1003 %CPU
   
   5. idle=mwait
      2188.06 ns/ctxsw -- 206.3 %CPU

Here is the data we get when running benchmark netperf:

   1. w/o patch:
      14556.8 bits/s  -- 144.2 %CPU

   2. w/ patch:
      halt_poll_threshold=10000 -- 15803.89 bits/s -- 159.5 %CPU
      halt_poll_threshold=20000 -- 15899.04 bits/s -- 161.5 %CPU
      halt_poll_threshold=30000 -- 15642.38 bits/s -- 161.8 %CPU
      halt_poll_threshold=40000 -- 18040.76 bits/s -- 184.0 %CPU
      halt_poll_threshold=50000 -- 18877.61 bits/s -- 197.3 %CPU

   3. kvm dynamic poll
      halt_poll_ns=10000 -- 15876.00 bits/s -- 172.2 %CPU
      halt_poll_ns=20000 -- 15602.58 bits/s -- 185.4 %CPU
      halt_poll_ns=30000 -- 15930.69 bits/s -- 194.4 %CPU
      halt_poll_ns=40000 -- 16413.09 bits/s -- 195.3 %CPU
      halt_poll_ns=50000 -- 16417.42 bits/s -- 196.3 %CPU

   4. idle=poll in guest
      18441.3bit/s -- 1003 %CPU

   5. idle=mwait in guest
      15760.6  bits/s  -- 157.6 %CPU

V1 -> V2:
- integrate the smart halt poll into paravirt code
- use idle_stamp instead of check_poll
- since it hard to get whether vcpu is the only task in pcpu, so we
  don't consider it in this series.(May improve it in future)

Yang Zhang (7):
  x86/paravirt: Add pv_idle_ops to paravirt ops
  KVM guest: register kvm_idle_poll for pv_idle_ops
  sched/idle: Add poll before enter real idle path
  x86/paravirt: Add update in x86/paravirt pv_idle_ops
  Documentation: Add three sysctls for smart idle poll
  KVM guest: introduce smart idle poll algorithm
  sched/idle: update poll time when wakeup from idle

 Documentation/sysctl/kernel.txt       | 25 +++++++++++++
 arch/x86/include/asm/paravirt.h       | 10 ++++++
 arch/x86/include/asm/paravirt_types.h |  7 ++++
 arch/x86/kernel/kvm.c                 | 67 +++++++++++++++++++++++++++++++++++
 arch/x86/kernel/paravirt.c            | 11 ++++++
 arch/x86/kernel/process.c             |  7 ++++
 include/linux/kernel.h                |  6 ++++
 include/linux/sched/idle.h            |  4 +++
 kernel/sched/core.c                   |  4 +++
 kernel/sched/idle.c                   |  9 +++++
 kernel/sysctl.c                       | 23 ++++++++++++
 11 files changed, 173 insertions(+)

-- 
1.8.3.1

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#1722396 — [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

Add poll in do_idle. For UP VM, if there are running task, it will not
goes into idle path, so we only enable poll in SMP VM.

Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
Signed-off-by: Quan Xu <quan.xu0@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kyle Huey <me@kylehuey.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Len Brown <len.brown@intel.com>
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/kernel/process.c | 7 +++++++
 kernel/sched/idle.c       | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 3ca1980..def4113 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -332,6 +332,13 @@ void arch_cpu_idle(void)
 	x86_idle();
 }
 
+#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT)
+void arch_cpu_idle_poll(void)
+{
+	paravirt_idle_poll();
+}
+#endif
+
 /*
  * We use this if we don't have any better idle routine..
  */
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 6c23e30..b374744 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -74,6 +74,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
 }
 
 /* Weak implementations for optional arch specific functions */
+void __weak arch_cpu_idle_poll(void) { }
 void __weak arch_cpu_idle_prepare(void) { }
 void __weak arch_cpu_idle_enter(void) { }
 void __weak arch_cpu_idle_exit(void) { }
@@ -219,6 +220,7 @@ static void do_idle(void)
 	 */
 
 	__current_set_polling();
+	arch_cpu_idle_poll();
 	quiet_vmstat();
 	tick_nohz_idle_enter();
 
-- 
1.8.3.1

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#1722440 — Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

On Tue, Aug 29, 2017 at 11:46:37AM +0000, Yang Zhang wrote:
> Add poll in do_idle. For UP VM, if there are running task, it will not
> goes into idle path, so we only enable poll in SMP VM.
> 
> Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
> Signed-off-by: Quan Xu <quan.xu0@gmail.com>

Broken SoB chain.

> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 6c23e30..b374744 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -74,6 +74,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
>  }
>  
>  /* Weak implementations for optional arch specific functions */
> +void __weak arch_cpu_idle_poll(void) { }
>  void __weak arch_cpu_idle_prepare(void) { }
>  void __weak arch_cpu_idle_enter(void) { }

And not a word on why we need a new arch hook. What's wrong with
arch_cpu_idle_enter() for instance?

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#1724796 — Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

on 2017/8/29 20:45, Peter Zijlstra wrote:

> On Tue, Aug 29, 2017 at 11:46:37AM +0000, Yang Zhang wrote:
>> Add poll in do_idle. For UP VM, if there are running task, it will not
>> goes into idle path, so we only enable poll in SMP VM.
>>
>> Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
>> Signed-off-by: Quan Xu <quan.xu0@gmail.com>
> Broken SoB chain.
   Peter,  I can't follow 'Broken SoB chain'.. could you more about it?

   -Quan

>> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
>> index 6c23e30..b374744 100644
>> --- a/kernel/sched/idle.c
>> +++ b/kernel/sched/idle.c
>> @@ -74,6 +74,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
>>   }
>>   
>>   /* Weak implementations for optional arch specific functions */
>> +void __weak arch_cpu_idle_poll(void) { }
>>   void __weak arch_cpu_idle_prepare(void) { }
>>   void __weak arch_cpu_idle_enter(void) { }
> And not a word on why we need a new arch hook. What's wrong with
> arch_cpu_idle_enter() for instance?

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#1722541 — Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

On Tue, Aug 29, 2017 at 11:46:37AM +0000, Yang Zhang wrote:
> Add poll in do_idle. For UP VM, if there are running task, it will not
> goes into idle path, so we only enable poll in SMP VM.
> 
> Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
> Signed-off-by: Quan Xu <quan.xu0@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: x86@kernel.org
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Kyle Huey <me@kylehuey.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Len Brown <len.brown@intel.com>
> Cc: linux-kernel@vger.kernel.org
> ---
>  arch/x86/kernel/process.c | 7 +++++++
>  kernel/sched/idle.c       | 2 ++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 3ca1980..def4113 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -332,6 +332,13 @@ void arch_cpu_idle(void)
>  	x86_idle();
>  }
>  
> +#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT)
> +void arch_cpu_idle_poll(void)
> +{
> +	paravirt_idle_poll();
> +}
> +#endif

So this will get called on any system which has CONFIG_PARAVIRT enabled
*even* if they're not running any guests.

Huh?

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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#1724819 — Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

on 2017/8/29 22:39, Borislav Petkov wrote:
> On Tue, Aug 29, 2017 at 11:46:37AM +0000, Yang Zhang wrote:
>> Add poll in do_idle. For UP VM, if there are running task, it will not
>> goes into idle path, so we only enable poll in SMP VM.
>>
>> Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
>> Signed-off-by: Quan Xu <quan.xu0@gmail.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: "H. Peter Anvin" <hpa@zytor.com>
>> Cc: x86@kernel.org
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Borislav Petkov <bp@alien8.de>
>> Cc: Kyle Huey <me@kylehuey.com>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: Len Brown <len.brown@intel.com>
>> Cc: linux-kernel@vger.kernel.org
>> ---
>>   arch/x86/kernel/process.c | 7 +++++++
>>   kernel/sched/idle.c       | 2 ++
>>   2 files changed, 9 insertions(+)
>>
>> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
>> index 3ca1980..def4113 100644
>> --- a/arch/x86/kernel/process.c
>> +++ b/arch/x86/kernel/process.c
>> @@ -332,6 +332,13 @@ void arch_cpu_idle(void)
>>   	x86_idle();
>>   }
>>   
>> +#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT)
>> +void arch_cpu_idle_poll(void)
>> +{
>> +	paravirt_idle_poll();
>> +}
>> +#endif
> So this will get called on any system which has CONFIG_PARAVIRT enabled
> *even* if they're not running any guests.
>
> Huh?
    Borislav ,
    yes,  this will get called on any system which has CONFIG_PARAVIRT 
enabled.

    but if they are not running any guests,  the callback is 
paravirt_nop() ,
    IIUC which is as similar as the other paravirt_*, such as 
paravirt_pgd_free()..

  - Quan

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#1722397 — [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops

So far, pv_idle_ops.poll is the only ops for pv_idle. .poll is called in
idle path which will polling for a while before we enter the real idle
state.

In virtualization, idle path includes several heavy operations
includes timer access(LAPIC timer or TSC deadline timer) which will hurt
performance especially for latency intensive workload like message
passing task. The cost is mainly come from the vmexit which is a
hardware context switch between VM and hypervisor. Our solution is to
poll for a while and do not enter real idle path if we can get the
schedule event during polling.

Poll may cause the CPU waste so we adopt a smart polling mechanism to
reduce the useless poll.

Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
Signed-off-by: Quan Xu <quan.xu0@gmail.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Alok Kataria <akataria@vmware.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: virtualization@lists.linux-foundation.org
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/include/asm/paravirt.h       | 5 +++++
 arch/x86/include/asm/paravirt_types.h | 6 ++++++
 arch/x86/kernel/paravirt.c            | 6 ++++++
 3 files changed, 17 insertions(+)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 9ccac19..6d46760 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -202,6 +202,11 @@ static inline unsigned long long paravirt_read_pmc(int counter)
 
 #define rdpmcl(counter, val) ((val) = paravirt_read_pmc(counter))
 
+static inline void paravirt_idle_poll(void)
+{
+	PVOP_VCALL0(pv_idle_ops.poll);
+}
+
 static inline void paravirt_alloc_ldt(struct desc_struct *ldt, unsigned entries)
 {
 	PVOP_VCALL2(pv_cpu_ops.alloc_ldt, ldt, entries);
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 9ffc36b..cf45726 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -324,6 +324,10 @@ struct pv_lock_ops {
 	struct paravirt_callee_save vcpu_is_preempted;
 } __no_randomize_layout;
 
+struct pv_idle_ops {
+	void (*poll)(void);
+} __no_randomize_layout;
+
 /* This contains all the paravirt structures: we get a convenient
  * number for each function using the offset which we use to indicate
  * what to patch. */
@@ -334,6 +338,7 @@ struct paravirt_patch_template {
 	struct pv_irq_ops pv_irq_ops;
 	struct pv_mmu_ops pv_mmu_ops;
 	struct pv_lock_ops pv_lock_ops;
+	struct pv_idle_ops pv_idle_ops;
 } __no_randomize_layout;
 
 extern struct pv_info pv_info;
@@ -343,6 +348,7 @@ struct paravirt_patch_template {
 extern struct pv_irq_ops pv_irq_ops;
 extern struct pv_mmu_ops pv_mmu_ops;
 extern struct pv_lock_ops pv_lock_ops;
+extern struct pv_idle_ops pv_idle_ops;
 
 #define PARAVIRT_PATCH(x)					\
 	(offsetof(struct paravirt_patch_template, x) / sizeof(void *))
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index bc0a849..1b5b247 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -128,6 +128,7 @@ static void *get_call_destination(u8 type)
 #ifdef CONFIG_PARAVIRT_SPINLOCKS
 		.pv_lock_ops = pv_lock_ops,
 #endif
+		.pv_idle_ops = pv_idle_ops,
 	};
 	return *((void **)&tmpl + type);
 }
@@ -312,6 +313,10 @@ struct pv_time_ops pv_time_ops = {
 	.steal_clock = native_steal_clock,
 };
 
+struct pv_idle_ops pv_idle_ops = {
+	.poll = paravirt_nop,
+};
+
 __visible struct pv_irq_ops pv_irq_ops = {
 	.save_fl = __PV_IS_CALLEE_SAVE(native_save_fl),
 	.restore_fl = __PV_IS_CALLEE_SAVE(native_restore_fl),
@@ -471,3 +476,4 @@ struct pv_mmu_ops pv_mmu_ops __ro_after_init = {
 EXPORT_SYMBOL    (pv_mmu_ops);
 EXPORT_SYMBOL_GPL(pv_info);
 EXPORT_SYMBOL    (pv_irq_ops);
+EXPORT_SYMBOL    (pv_idle_ops);
-- 
1.8.3.1

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#1722514 — Re: [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops

On Tue, Aug 29, 2017 at 11:46:35AM +0000, Yang Zhang wrote:
> So far, pv_idle_ops.poll is the only ops for pv_idle. .poll is called in
> idle path which will polling for a while before we enter the real idle
> state.
> 
> In virtualization, idle path includes several heavy operations
> includes timer access(LAPIC timer or TSC deadline timer) which will hurt
> performance especially for latency intensive workload like message
> passing task. The cost is mainly come from the vmexit which is a
> hardware context switch between VM and hypervisor. Our solution is to
> poll for a while and do not enter real idle path if we can get the
> schedule event during polling.
> 
> Poll may cause the CPU waste so we adopt a smart polling mechanism to
> reduce the useless poll.
> 
> Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
> Signed-off-by: Quan Xu <quan.xu0@gmail.com>
> Cc: Jeremy Fitzhardinge <jeremy@goop.org>
> Cc: Chris Wright <chrisw@sous-sol.org>
> Cc: Alok Kataria <akataria@vmware.com>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: x86@kernel.org
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: virtualization@lists.linux-foundation.org
> Cc: linux-kernel@vger.kernel.org

Adding xen-devel.

Juergen, we really should replace Jeremy's name with xen-devel or
your name.. Wasn't there an patch by you that took some of the 
mainternship over it?

> ---
>  arch/x86/include/asm/paravirt.h       | 5 +++++
>  arch/x86/include/asm/paravirt_types.h | 6 ++++++
>  arch/x86/kernel/paravirt.c            | 6 ++++++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index 9ccac19..6d46760 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -202,6 +202,11 @@ static inline unsigned long long paravirt_read_pmc(int counter)
>  
>  #define rdpmcl(counter, val) ((val) = paravirt_read_pmc(counter))
>  
> +static inline void paravirt_idle_poll(void)
> +{
> +	PVOP_VCALL0(pv_idle_ops.poll);
> +}
> +
>  static inline void paravirt_alloc_ldt(struct desc_struct *ldt, unsigned entries)
>  {
>  	PVOP_VCALL2(pv_cpu_ops.alloc_ldt, ldt, entries);
> diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
> index 9ffc36b..cf45726 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -324,6 +324,10 @@ struct pv_lock_ops {
>  	struct paravirt_callee_save vcpu_is_preempted;
>  } __no_randomize_layout;
>  
> +struct pv_idle_ops {
> +	void (*poll)(void);
> +} __no_randomize_layout;
> +
>  /* This contains all the paravirt structures: we get a convenient
>   * number for each function using the offset which we use to indicate
>   * what to patch. */
> @@ -334,6 +338,7 @@ struct paravirt_patch_template {
>  	struct pv_irq_ops pv_irq_ops;
>  	struct pv_mmu_ops pv_mmu_ops;
>  	struct pv_lock_ops pv_lock_ops;
> +	struct pv_idle_ops pv_idle_ops;
>  } __no_randomize_layout;
>  
>  extern struct pv_info pv_info;
> @@ -343,6 +348,7 @@ struct paravirt_patch_template {
>  extern struct pv_irq_ops pv_irq_ops;
>  extern struct pv_mmu_ops pv_mmu_ops;
>  extern struct pv_lock_ops pv_lock_ops;
> +extern struct pv_idle_ops pv_idle_ops;
>  
>  #define PARAVIRT_PATCH(x)					\
>  	(offsetof(struct paravirt_patch_template, x) / sizeof(void *))
> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> index bc0a849..1b5b247 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -128,6 +128,7 @@ static void *get_call_destination(u8 type)
>  #ifdef CONFIG_PARAVIRT_SPINLOCKS
>  		.pv_lock_ops = pv_lock_ops,
>  #endif
> +		.pv_idle_ops = pv_idle_ops,
>  	};
>  	return *((void **)&tmpl + type);
>  }
> @@ -312,6 +313,10 @@ struct pv_time_ops pv_time_ops = {
>  	.steal_clock = native_steal_clock,
>  };
>  
> +struct pv_idle_ops pv_idle_ops = {
> +	.poll = paravirt_nop,
> +};
> +
>  __visible struct pv_irq_ops pv_irq_ops = {
>  	.save_fl = __PV_IS_CALLEE_SAVE(native_save_fl),
>  	.restore_fl = __PV_IS_CALLEE_SAVE(native_restore_fl),
> @@ -471,3 +476,4 @@ struct pv_mmu_ops pv_mmu_ops __ro_after_init = {
>  EXPORT_SYMBOL    (pv_mmu_ops);
>  EXPORT_SYMBOL_GPL(pv_info);
>  EXPORT_SYMBOL    (pv_irq_ops);
> +EXPORT_SYMBOL    (pv_idle_ops);
> -- 
> 1.8.3.1
> 

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#1723073 — Re: [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops

On 29/08/17 15:55, Konrad Rzeszutek Wilk wrote:
> On Tue, Aug 29, 2017 at 11:46:35AM +0000, Yang Zhang wrote:
>> So far, pv_idle_ops.poll is the only ops for pv_idle. .poll is called in
>> idle path which will polling for a while before we enter the real idle
>> state.
>>
>> In virtualization, idle path includes several heavy operations
>> includes timer access(LAPIC timer or TSC deadline timer) which will hurt
>> performance especially for latency intensive workload like message
>> passing task. The cost is mainly come from the vmexit which is a
>> hardware context switch between VM and hypervisor. Our solution is to
>> poll for a while and do not enter real idle path if we can get the
>> schedule event during polling.
>>
>> Poll may cause the CPU waste so we adopt a smart polling mechanism to
>> reduce the useless poll.
>>
>> Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
>> Signed-off-by: Quan Xu <quan.xu0@gmail.com>
>> Cc: Jeremy Fitzhardinge <jeremy@goop.org>
>> Cc: Chris Wright <chrisw@sous-sol.org>
>> Cc: Alok Kataria <akataria@vmware.com>
>> Cc: Rusty Russell <rusty@rustcorp.com.au>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: "H. Peter Anvin" <hpa@zytor.com>
>> Cc: x86@kernel.org
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>> Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: virtualization@lists.linux-foundation.org
>> Cc: linux-kernel@vger.kernel.org
> 
> Adding xen-devel.
> 
> Juergen, we really should replace Jeremy's name with xen-devel or
> your name..

I wouldn't mind being added. What does Jeremy think of being removed?

> Wasn't there an patch by you that took some of the 
> mainternship over it?

I added include/linux/hypervisor.h to the PARAVIRT section and offered
to maintain it in case the PARAVIRT maintainers didn't want to.


Juergen

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#1724810 — Re: [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops

On 2017/8/29 21:55, Konrad Rzeszutek Wilk wrote:
> On Tue, Aug 29, 2017 at 11:46:35AM +0000, Yang Zhang wrote:
>> So far, pv_idle_ops.poll is the only ops for pv_idle. .poll is called in
>> idle path which will polling for a while before we enter the real idle
>> state.
>>
>> In virtualization, idle path includes several heavy operations
>> includes timer access(LAPIC timer or TSC deadline timer) which will hurt
>> performance especially for latency intensive workload like message
>> passing task. The cost is mainly come from the vmexit which is a
>> hardware context switch between VM and hypervisor. Our solution is to
>> poll for a while and do not enter real idle path if we can get the
>> schedule event during polling.
>>
>> Poll may cause the CPU waste so we adopt a smart polling mechanism to
>> reduce the useless poll.
>>
>> Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
>> Signed-off-by: Quan Xu <quan.xu0@gmail.com>
>> Cc: Jeremy Fitzhardinge <jeremy@goop.org>
>> Cc: Chris Wright <chrisw@sous-sol.org>
>> Cc: Alok Kataria <akataria@vmware.com>
>> Cc: Rusty Russell <rusty@rustcorp.com.au>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: "H. Peter Anvin" <hpa@zytor.com>
>> Cc: x86@kernel.org
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>> Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: virtualization@lists.linux-foundation.org
>> Cc: linux-kernel@vger.kernel.org
> 
> Adding xen-devel.
> 
> Juergen, we really should replace Jeremy's name with xen-devel or
> your name.. Wasn't there an patch by you that took some of the
> mainternship over it?

Hi Konard, I didn't test it in Xen side since i don't have the 
environment but i can add it for Xen in next version if you think it is 
useful to Xen as well.

> 
>> ---
>>   arch/x86/include/asm/paravirt.h       | 5 +++++
>>   arch/x86/include/asm/paravirt_types.h | 6 ++++++
>>   arch/x86/kernel/paravirt.c            | 6 ++++++
>>   3 files changed, 17 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
>> index 9ccac19..6d46760 100644
>> --- a/arch/x86/include/asm/paravirt.h
>> +++ b/arch/x86/include/asm/paravirt.h
>> @@ -202,6 +202,11 @@ static inline unsigned long long paravirt_read_pmc(int counter)
>>   
>>   #define rdpmcl(counter, val) ((val) = paravirt_read_pmc(counter))
>>   
>> +static inline void paravirt_idle_poll(void)
>> +{
>> +	PVOP_VCALL0(pv_idle_ops.poll);
>> +}
>> +
>>   static inline void paravirt_alloc_ldt(struct desc_struct *ldt, unsigned entries)
>>   {
>>   	PVOP_VCALL2(pv_cpu_ops.alloc_ldt, ldt, entries);
>> diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
>> index 9ffc36b..cf45726 100644
>> --- a/arch/x86/include/asm/paravirt_types.h
>> +++ b/arch/x86/include/asm/paravirt_types.h
>> @@ -324,6 +324,10 @@ struct pv_lock_ops {
>>   	struct paravirt_callee_save vcpu_is_preempted;
>>   } __no_randomize_layout;
>>   
>> +struct pv_idle_ops {
>> +	void (*poll)(void);
>> +} __no_randomize_layout;
>> +
>>   /* This contains all the paravirt structures: we get a convenient
>>    * number for each function using the offset which we use to indicate
>>    * what to patch. */
>> @@ -334,6 +338,7 @@ struct paravirt_patch_template {
>>   	struct pv_irq_ops pv_irq_ops;
>>   	struct pv_mmu_ops pv_mmu_ops;
>>   	struct pv_lock_ops pv_lock_ops;
>> +	struct pv_idle_ops pv_idle_ops;
>>   } __no_randomize_layout;
>>   
>>   extern struct pv_info pv_info;
>> @@ -343,6 +348,7 @@ struct paravirt_patch_template {
>>   extern struct pv_irq_ops pv_irq_ops;
>>   extern struct pv_mmu_ops pv_mmu_ops;
>>   extern struct pv_lock_ops pv_lock_ops;
>> +extern struct pv_idle_ops pv_idle_ops;
>>   
>>   #define PARAVIRT_PATCH(x)					\
>>   	(offsetof(struct paravirt_patch_template, x) / sizeof(void *))
>> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
>> index bc0a849..1b5b247 100644
>> --- a/arch/x86/kernel/paravirt.c
>> +++ b/arch/x86/kernel/paravirt.c
>> @@ -128,6 +128,7 @@ static void *get_call_destination(u8 type)
>>   #ifdef CONFIG_PARAVIRT_SPINLOCKS
>>   		.pv_lock_ops = pv_lock_ops,
>>   #endif
>> +		.pv_idle_ops = pv_idle_ops,
>>   	};
>>   	return *((void **)&tmpl + type);
>>   }
>> @@ -312,6 +313,10 @@ struct pv_time_ops pv_time_ops = {
>>   	.steal_clock = native_steal_clock,
>>   };
>>   
>> +struct pv_idle_ops pv_idle_ops = {
>> +	.poll = paravirt_nop,
>> +};
>> +
>>   __visible struct pv_irq_ops pv_irq_ops = {
>>   	.save_fl = __PV_IS_CALLEE_SAVE(native_save_fl),
>>   	.restore_fl = __PV_IS_CALLEE_SAVE(native_restore_fl),
>> @@ -471,3 +476,4 @@ struct pv_mmu_ops pv_mmu_ops __ro_after_init = {
>>   EXPORT_SYMBOL    (pv_mmu_ops);
>>   EXPORT_SYMBOL_GPL(pv_info);
>>   EXPORT_SYMBOL    (pv_irq_ops);
>> +EXPORT_SYMBOL    (pv_idle_ops);
>> -- 
>> 1.8.3.1
>>


-- 
Yang
Alibaba Cloud Computing

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#1722400 — [RFC PATCH v2 5/7] Documentation: Add three sysctls for smart idle poll

To reduce the cost of poll, we introduce three sysctl to control the
poll time.

Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
Signed-off-by: Quan Xu <quan.xu0@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Alok Kataria <akataria@vmware.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jessica Yu <jeyu@redhat.com>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Cc: zijun_hu <zijun_hu@htc.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Cc: linux-fsdevel@vger.kernel.org
---
 Documentation/sysctl/kernel.txt | 25 +++++++++++++++++++++++++
 arch/x86/kernel/paravirt.c      |  4 ++++
 include/linux/kernel.h          |  6 ++++++
 kernel/sysctl.c                 | 23 +++++++++++++++++++++++
 4 files changed, 58 insertions(+)

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index bac23c1..67447b8 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -63,6 +63,9 @@ show up in /proc/sys/kernel:
 - perf_event_max_stack
 - perf_event_max_contexts_per_stack
 - pid_max
+- poll_grow                   [ X86 only ]
+- poll_shrink                 [ X86 only ]
+- poll_threshold_ns           [ X86 only ]
 - powersave-nap               [ PPC only ]
 - printk
 - printk_delay
@@ -702,6 +705,28 @@ kernel tries to allocate a number starting from this one.
 
 ==============================================================
 
+poll_grow: (X86 only)
+
+This parameter is multiplied in the grow_poll_ns() to increase the poll time.
+By default, the values is 2.
+
+==============================================================
+poll_shrink: (X86 only)
+
+This parameter is divided in the shrink_poll_ns() to reduce the poll time.
+By default, the values is 2.
+
+==============================================================
+poll_threshold_ns: (X86 only)
+
+This parameter controls the max poll time before entering real idle path.
+This parameter is expected to take effect only when running inside a VM.
+It would make no sense to turn on it in bare mental.
+By default, the values is 0 means don't poll. It is recommended to change
+the value to non-zero if running latency-bound workloads inside VM.
+
+==============================================================
+
 powersave-nap: (PPC only)
 
 If set, Linux-PPC will use the 'nap' mode of powersaving,
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index a11b2c2..0b92f8f 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -318,6 +318,10 @@ struct pv_idle_ops pv_idle_ops = {
 	.update = paravirt_nop,
 };
 
+unsigned long poll_threshold_ns;
+unsigned int poll_shrink = 2;
+unsigned int poll_grow = 2;
+
 __visible struct pv_irq_ops pv_irq_ops = {
 	.save_fl = __PV_IS_CALLEE_SAVE(native_save_fl),
 	.restore_fl = __PV_IS_CALLEE_SAVE(native_restore_fl),
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index bd6d96c..6cb2820 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -462,6 +462,12 @@ extern __scanf(2, 0)
 
 extern bool crash_kexec_post_notifiers;
 
+#ifdef CONFIG_PARAVIRT
+extern unsigned long poll_threshold_ns;
+extern unsigned int poll_shrink;
+extern unsigned int poll_grow;
+#endif
+
 /*
  * panic_cpu is used for synchronizing panic() and crash_kexec() execution. It
  * holds a CPU number which is executing panic() currently. A value of
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 6648fbb..9b86a8f 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1229,6 +1229,29 @@ static int sysrq_sysctl_handler(struct ctl_table *table, int write,
 		.extra2		= &one,
 	},
 #endif
+#ifdef CONFIG_PARAVIRT
+	{
+		.procname       = "halt_poll_threshold",
+		.data           = &poll_threshold_ns,
+		.maxlen         = sizeof(unsigned long),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
+	{
+		.procname       = "halt_poll_grow",
+		.data           = &poll_grow,
+		.maxlen         = sizeof(unsigned int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
+	{
+		.procname       = "halt_poll_shrink",
+		.data           = &poll_shrink,
+		.maxlen         = sizeof(unsigned int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
+#endif
 	{ }
 };
 
-- 
1.8.3.1

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#1722637 — Re: [RFC PATCH v2 5/7] Documentation: Add three sysctls for smart idle poll

On Tue, Aug 29, 2017 at 11:46:39AM +0000, Yang Zhang wrote:
> To reduce the cost of poll, we introduce three sysctl to control the
> poll time.

This commit does not describe in any way the fact that these knobs are
all for and only for PARAVIRT.

> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
> index bac23c1..67447b8 100644
> --- a/Documentation/sysctl/kernel.txt
> +++ b/Documentation/sysctl/kernel.txt
> @@ -63,6 +63,9 @@ show up in /proc/sys/kernel:
>  - perf_event_max_stack
>  - perf_event_max_contexts_per_stack
>  - pid_max
> +- poll_grow                   [ X86 only ]
> +- poll_shrink                 [ X86 only ]
> +- poll_threshold_ns           [ X86 only ]

How about paravirt_ prefix?

>  - powersave-nap               [ PPC only ]
>  - printk
>  - printk_delay
> @@ -702,6 +705,28 @@ kernel tries to allocate a number starting from this one.
>  
>  ==============================================================
>  
> +poll_grow: (X86 only)
> +
> +This parameter is multiplied in the grow_poll_ns() to increase the poll time.
> +By default, the values is 2.
> +
> +==============================================================
> +poll_shrink: (X86 only)
> +
> +This parameter is divided in the shrink_poll_ns() to reduce the poll time.
> +By default, the values is 2.

These don't say anything about this being related to paravirt.

> +
> +==============================================================
> +poll_threshold_ns: (X86 only)
> +
> +This parameter controls the max poll time before entering real idle path.
> +This parameter is expected to take effect only when running inside a VM.
> +It would make no sense to turn on it in bare mental.

turn it on? Or modify, or use it?

> +By default, the values is 0 means don't poll. It is recommended to change
> +the value to non-zero if running latency-bound workloads inside VM.
> +
> +==============================================================
> +
>  powersave-nap: (PPC only)
>  
>  If set, Linux-PPC will use the 'nap' mode of powersaving,
> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> index a11b2c2..0b92f8f 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -318,6 +318,10 @@ struct pv_idle_ops pv_idle_ops = {
>  	.update = paravirt_nop,
>  };
>  
> +unsigned long poll_threshold_ns;
> +unsigned int poll_shrink = 2;
> +unsigned int poll_grow = 2;
> +
>  __visible struct pv_irq_ops pv_irq_ops = {
>  	.save_fl = __PV_IS_CALLEE_SAVE(native_save_fl),
>  	.restore_fl = __PV_IS_CALLEE_SAVE(native_restore_fl),
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index bd6d96c..6cb2820 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -462,6 +462,12 @@ extern __scanf(2, 0)
>  
>  extern bool crash_kexec_post_notifiers;
>  
> +#ifdef CONFIG_PARAVIRT
> +extern unsigned long poll_threshold_ns;
> +extern unsigned int poll_shrink;
> +extern unsigned int poll_grow;
> +#endif

What are these if we are on bare metal but support
paravirt? The docs are not clear in any way about it.

> +
>  /*
>   * panic_cpu is used for synchronizing panic() and crash_kexec() execution. It
>   * holds a CPU number which is executing panic() currently. A value of
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 6648fbb..9b86a8f 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1229,6 +1229,29 @@ static int sysrq_sysctl_handler(struct ctl_table *table, int write,
>  		.extra2		= &one,
>  	},
>  #endif
> +#ifdef CONFIG_PARAVIRT
> +	{
> +		.procname       = "halt_poll_threshold",
> +		.data           = &poll_threshold_ns,
> +		.maxlen         = sizeof(unsigned long),
> +		.mode           = 0644,
> +		.proc_handler   = proc_dointvec,
> +	},

proc_doulongvec_minmax() may be more appropriate here? What is the range?
Also what user did you see used proc_dointvec() but had unsigned long?
If the test below reveal this is invalid we would need to go fix them
as well.

> +	{
> +		.procname       = "halt_poll_grow",
> +		.data           = &poll_grow,
> +		.maxlen         = sizeof(unsigned int),
> +		.mode           = 0644,
> +		.proc_handler   = proc_dointvec,
> +	},
> +	{
> +		.procname       = "halt_poll_shrink",
> +		.data           = &poll_shrink,
> +		.maxlen         = sizeof(unsigned int),
> +		.mode           = 0644,
> +		.proc_handler   = proc_dointvec,

We have now a much more appropriate proc_douintvec() proc_douintvec_minmax().
It seems you want to support only unsigned int for two of these so that would
be more appropriate.

To test things out you can replicate your values using or extending the
test driver lib/test_sysctl.c CONFIG_TEST_SYSCTL=m with your type of
values and then fuzz testing them with arbitrary values to ensure you get
only as input what you really think these values should get.

Once done please extend the script:

tools/testing/selftests/sysctl/sysctl.sh

to cover the different tests you have run, we want tests to be generic.

  Luis

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#1722401 — [RFC PATCH v2 2/7] KVM guest: register kvm_idle_poll for pv_idle_ops

Although smart idle poll has nothing to do with paravirt, it can not
bring any benifit to native. So we only enable it when Linux runs as a
KVM guest(it can extend to other hypervisor like Xen, HyperV and
VMware).

Introduce per-CPU variable poll_duration_ns to control the max poll
time.

Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
Signed-off-by: Quan Xu <quan.xu0@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/kernel/kvm.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index d04e30e..7d84a02 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -75,6 +75,7 @@ static int parse_no_kvmclock_vsyscall(char *arg)
 
 early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
 
+static DEFINE_PER_CPU(unsigned long, poll_duration_ns);
 static DEFINE_PER_CPU(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
 static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
 static int has_steal_clock = 0;
@@ -357,6 +358,29 @@ static void kvm_guest_cpu_init(void)
 		kvm_register_steal_time();
 }
 
+static void kvm_idle_poll(void)
+{
+	unsigned long poll_duration = this_cpu_read(poll_duration_ns);
+	ktime_t start, cur, stop;
+
+	start = cur = ktime_get();
+	stop = ktime_add_ns(ktime_get(), poll_duration);
+
+	do {
+		if (need_resched())
+			break;
+		cur = ktime_get();
+	} while (ktime_before(cur, stop));
+}
+
+static void kvm_guest_idle_init(void)
+{
+	if (!kvm_para_available())
+		return;
+
+	pv_idle_ops.poll = kvm_idle_poll;
+}
+
 static void kvm_pv_disable_apf(void)
 {
 	if (!__this_cpu_read(apf_reason.enabled))
@@ -492,6 +516,8 @@ void __init kvm_guest_init(void)
 	kvm_guest_cpu_init();
 #endif
 
+	kvm_guest_idle_init();
+
 	/*
 	 * Hard lockup detection is enabled by default. Disable it, as guests
 	 * can get false positives too easily, for example if the host is
-- 
1.8.3.1

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#1722403 — [RFC PATCH v2 4/7] x86/paravirt: Add update in x86/paravirt pv_idle_ops

.update is used to adjust the next poll time.

Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
Signed-off-by: Quan Xu <quan.xu0@gmail.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Alok Kataria <akataria@vmware.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: virtualization@lists.linux-foundation.org
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/include/asm/paravirt.h       | 5 +++++
 arch/x86/include/asm/paravirt_types.h | 1 +
 arch/x86/kernel/paravirt.c            | 1 +
 3 files changed, 7 insertions(+)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 6d46760..32e1c06 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -207,6 +207,11 @@ static inline void paravirt_idle_poll(void)
 	PVOP_VCALL0(pv_idle_ops.poll);
 }
 
+static inline void paravirt_idle_update_poll_duration(unsigned long duration)
+{
+	PVOP_VCALL1(pv_idle_ops.update, duration);
+}
+
 static inline void paravirt_alloc_ldt(struct desc_struct *ldt, unsigned entries)
 {
 	PVOP_VCALL2(pv_cpu_ops.alloc_ldt, ldt, entries);
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index cf45726..3b4f95a 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -326,6 +326,7 @@ struct pv_lock_ops {
 
 struct pv_idle_ops {
 	void (*poll)(void);
+	void (*update)(unsigned long);
 } __no_randomize_layout;
 
 /* This contains all the paravirt structures: we get a convenient
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 1b5b247..a11b2c2 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -315,6 +315,7 @@ struct pv_time_ops pv_time_ops = {
 
 struct pv_idle_ops pv_idle_ops = {
 	.poll = paravirt_nop,
+	.update = paravirt_nop,
 };
 
 __visible struct pv_irq_ops pv_irq_ops = {
-- 
1.8.3.1

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#1722405 — [RFC PATCH v2 7/7] sched/idle: update poll time when wakeup from idle

In ttwu_do_wakeup, it will update avg_idle when wakeup from idle. Here
we just reuse this logic to update the poll time. It may be a little
late to update the poll in ttwu_do_wakeup, but the test result shows no
obvious performance gap compare with updating poll in irq handler.

one problem is that idle_stamp only used when using CFS scheduler. But
it is ok since it is the default policy for scheduler and only consider
it should enough.

Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
Signed-off-by: Quan Xu <quan.xu0@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
---
 include/linux/sched/idle.h | 4 ++++
 kernel/sched/core.c        | 4 ++++
 kernel/sched/idle.c        | 7 +++++++
 3 files changed, 15 insertions(+)

diff --git a/include/linux/sched/idle.h b/include/linux/sched/idle.h
index 5ca63eb..6e0554d 100644
--- a/include/linux/sched/idle.h
+++ b/include/linux/sched/idle.h
@@ -12,6 +12,10 @@ enum cpu_idle_type {
 
 extern void wake_up_if_idle(int cpu);
 
+#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT)
+extern void update_poll_duration(unsigned long idle_duration);
+#endif
+
 /*
  * Idle thread specific functions to determine the need_resched
  * polling state.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0869b20..25be9a3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1678,6 +1678,10 @@ static void ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags,
 		if (rq->avg_idle > max)
 			rq->avg_idle = max;
 
+#if defined(CONFIG_PARAVIRT)
+		update_poll_duration(rq->avg_idle);
+#endif
+
 		rq->idle_stamp = 0;
 	}
 #endif
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index b374744..7eb8559 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -101,6 +101,13 @@ void __cpuidle default_idle_call(void)
 	}
 }
 
+#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT)
+void update_poll_duration(unsigned long idle_duration)
+{
+	paravirt_idle_update_poll_duration(idle_duration);
+}
+#endif
+
 static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 		      int next_state)
 {
-- 
1.8.3.1

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#1722446 — Re: [RFC PATCH v2 7/7] sched/idle: update poll time when wakeup from idle

On Tue, Aug 29, 2017 at 11:46:41AM +0000, Yang Zhang wrote:
> In ttwu_do_wakeup, it will update avg_idle when wakeup from idle. Here
> we just reuse this logic to update the poll time. It may be a little
> late to update the poll in ttwu_do_wakeup, but the test result shows no
> obvious performance gap compare with updating poll in irq handler.
> 
> one problem is that idle_stamp only used when using CFS scheduler. But
> it is ok since it is the default policy for scheduler and only consider
> it should enough.
> 
> Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
> Signed-off-by: Quan Xu <quan.xu0@gmail.com>

Same broken SoB chain, and not a useful word on why you need to adjust
this crap to begin with. What you want that poll duration to be related
to is the cost of a VMEXIT/VMENTER cycle, not however long we happened
to be idle.

So no.

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#1724835 — Re: [RFC PATCH v2 7/7] sched/idle: update poll time when wakeup from idle

On 2017/8/29 20:46, Peter Zijlstra wrote:
> On Tue, Aug 29, 2017 at 11:46:41AM +0000, Yang Zhang wrote:
>> In ttwu_do_wakeup, it will update avg_idle when wakeup from idle. Here
>> we just reuse this logic to update the poll time. It may be a little
>> late to update the poll in ttwu_do_wakeup, but the test result shows no
>> obvious performance gap compare with updating poll in irq handler.
>>
>> one problem is that idle_stamp only used when using CFS scheduler. But
>> it is ok since it is the default policy for scheduler and only consider
>> it should enough.
>>
>> Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
>> Signed-off-by: Quan Xu <quan.xu0@gmail.com>
> 
> Same broken SoB chain, and not a useful word on why you need to adjust
> this crap to begin with. What you want that poll duration to be related
> to is the cost of a VMEXIT/VMENTER cycle, not however long we happened
> to be idle.

Actually, we should compare the cost of VMEXIT/VMENTER with the real 
duration in idle. We have a rough number of the cost for one 
VMEXIT/VMENTER(it is about 2k~4k cycles depends on the underlying CPU) 
and it introduces 4~5 VMENTER/VMEXITs in idle path which may increase 
about 7us latency in average. So we set the poll duration to 10us by 
default.

Another problem is there is no good way to measure the duration in idle. 
avg_idle is the only way i find so far. Do you have any suggestion to do 
it better? Thanks.

-- 
Yang
Alibaba Cloud Computing

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#1722410

On 08/29/2017 01:46 PM, Yang Zhang wrote:
> Some latency-intensive workload will see obviously performance
> drop when running inside VM. The main reason is that the overhead
> is amplified when running inside VM. The most cost i have seen is
> inside idle path.
>
> This patch introduces a new mechanism to poll for a while before
> entering idle state. If schedule is needed during poll, then we
> don't need to goes through the heavy overhead path.
>
> Here is the data we get when running benchmark contextswitch to measure
> the latency(lower is better):
>
>     1. w/o patch:
>        2493.14 ns/ctxsw -- 200.3 %CPU
>     
>     2. w/ patch:
>        halt_poll_threshold=10000 -- 1485.96ns/ctxsw -- 201.0 %CPU
>        halt_poll_threshold=20000 -- 1391.26 ns/ctxsw -- 200.7 %CPU
>        halt_poll_threshold=30000 -- 1488.55 ns/ctxsw -- 200.1 %CPU
>        halt_poll_threshold=500000 -- 1159.14 ns/ctxsw -- 201.5 %CPU
>     
>     3. kvm dynamic poll
>        halt_poll_ns=10000 -- 2296.11 ns/ctxsw -- 201.2 %CPU
>        halt_poll_ns=20000 -- 2599.7 ns/ctxsw -- 201.7 %CPU
>        halt_poll_ns=30000 -- 2588.68 ns/ctxsw -- 211.6 %CPU
>        halt_poll_ns=500000 -- 2423.20 ns/ctxsw -- 229.2 %CPU
>     
>     4. idle=poll
>        2050.1 ns/ctxsw -- 1003 %CPU
>     
>     5. idle=mwait
>        2188.06 ns/ctxsw -- 206.3 %CPU

Could you please try to create another metric for guest initiated, host 
aborted mwait?

For a quick benchmark, reserve 4 registers for a magic value, set them 
to the magic value before you enter MWAIT in the guest. Then allow 
native MWAIT execution on the host. If you see the guest wants to enter 
with the 4 registers containing the magic contents and no events are 
pending, directly go into the vcpu block function on the host.

That way any time a guest gets naturally aborted while in mwait, it will 
only reenter mwait when an event actually occured. While the guest is 
normally running (and nobody else wants to run on the host), we just 
stay in guest context, but with a sleeping CPU.

Overall, that might give us even better performance, as it allows for 
turbo boost and HT to work properly.


Alex

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#1724801

On 2017/8/29 19:58, Alexander Graf wrote:
> On 08/29/2017 01:46 PM, Yang Zhang wrote:
>> Some latency-intensive workload will see obviously performance
>> drop when running inside VM. The main reason is that the overhead
>> is amplified when running inside VM. The most cost i have seen is
>> inside idle path.
>>
>> This patch introduces a new mechanism to poll for a while before
>> entering idle state. If schedule is needed during poll, then we
>> don't need to goes through the heavy overhead path.
>>
>> Here is the data we get when running benchmark contextswitch to measure
>> the latency(lower is better):
>>
>>     1. w/o patch:
>>        2493.14 ns/ctxsw -- 200.3 %CPU
>>     2. w/ patch:
>>        halt_poll_threshold=10000 -- 1485.96ns/ctxsw -- 201.0 %CPU
>>        halt_poll_threshold=20000 -- 1391.26 ns/ctxsw -- 200.7 %CPU
>>        halt_poll_threshold=30000 -- 1488.55 ns/ctxsw -- 200.1 %CPU
>>        halt_poll_threshold=500000 -- 1159.14 ns/ctxsw -- 201.5 %CPU
>>     3. kvm dynamic poll
>>        halt_poll_ns=10000 -- 2296.11 ns/ctxsw -- 201.2 %CPU
>>        halt_poll_ns=20000 -- 2599.7 ns/ctxsw -- 201.7 %CPU
>>        halt_poll_ns=30000 -- 2588.68 ns/ctxsw -- 211.6 %CPU
>>        halt_poll_ns=500000 -- 2423.20 ns/ctxsw -- 229.2 %CPU
>>     4. idle=poll
>>        2050.1 ns/ctxsw -- 1003 %CPU
>>     5. idle=mwait
>>        2188.06 ns/ctxsw -- 206.3 %CPU
> 
> Could you please try to create another metric for guest initiated, host 
> aborted mwait?
> 
> For a quick benchmark, reserve 4 registers for a magic value, set them 
> to the magic value before you enter MWAIT in the guest. Then allow 
> native MWAIT execution on the host. If you see the guest wants to enter 

I guess you want to allow native MWAIT execution on the guest not host?

> with the 4 registers containing the magic contents and no events are 
> pending, directly go into the vcpu block function on the host.

Mmm..It is not very clear to me. If guest executes MWAIT without vmexit, 
how to check the register?

> 
> That way any time a guest gets naturally aborted while in mwait, it will 
> only reenter mwait when an event actually occured. While the guest is 
> normally running (and nobody else wants to run on the host), we just 
> stay in guest context, but with a sleeping CPU.
> 
> Overall, that might give us even better performance, as it allows for 
> turbo boost and HT to work properly.

In our testing,  we have enough cores(32cores) but only 10VCPUs, so in 
the best case, we may see the same performance as poll.

-- 
Yang
Alibaba Cloud Computing

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#1722454

Yang Zhang <yang.zhang.wz@gmail.com> writes:

> Some latency-intensive workload will see obviously performance 
> drop when running inside VM. The main reason is that the overhead 
> is amplified when running inside VM. The most cost i have seen is 
> inside idle path. 

You could test with https://lkml.org/lkml/2017/7/9/204
which optimizes these idle paths with a fast path.

If that works it would be a far better solution than
explicit tunables and basically giving up by polling.

-Andi

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