Re: [PATCH v2 0/4] implement vcpu preempted check

From	Paolo Bonzini <pbonzini@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 0/4] implement vcpu preempted check
Date	2016-07-06 14:40 +0200
Message-ID	<rRUhs-Lb-13@gated-at.bofh.it> (permalink)
References	<rOYKC-5Nk-11@gated-at.bofh.it> <rROYp-5Ma-3@gated-at.bofh.it> <rRSyZ-850-11@gated-at.bofh.it> <rRTOp-Bq-3@gated-at.bofh.it>
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On 06/07/2016 14:08, Wanpeng Li wrote:
> 2016-07-06 18:44 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>>
>>
>> On 06/07/2016 08:52, Peter Zijlstra wrote:
>>> On Tue, Jun 28, 2016 at 10:43:07AM -0400, Pan Xinhui wrote:
>>>> change fomr v1:
>>>>      a simplier definition of default vcpu_is_preempted
>>>>      skip mahcine type check on ppc, and add config. remove dedicated macro.
>>>>      add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner.
>>>>      add more comments
>>>>      thanks boqun and Peter's suggestion.
>>>>
>>>> This patch set aims to fix lock holder preemption issues.
>>>>
>>>> test-case:
>>>> perf record -a perf bench sched messaging -g 400 -p && perf report
>>>>
>>>> 18.09%  sched-messaging  [kernel.vmlinux]  [k] osq_lock
>>>> 12.28%  sched-messaging  [kernel.vmlinux]  [k] rwsem_spin_on_owner
>>>>  5.27%  sched-messaging  [kernel.vmlinux]  [k] mutex_unlock
>>>>  3.89%  sched-messaging  [kernel.vmlinux]  [k] wait_consider_task
>>>>  3.64%  sched-messaging  [kernel.vmlinux]  [k] _raw_write_lock_irq
>>>>  3.41%  sched-messaging  [kernel.vmlinux]  [k] mutex_spin_on_owner.is
>>>>  2.49%  sched-messaging  [kernel.vmlinux]  [k] system_call
>>>>
>>>> We introduce interface bool vcpu_is_preempted(int cpu) and use it in some spin
>>>> loops of osq_lock, rwsem_spin_on_owner and mutex_spin_on_owner.
>>>> These spin_on_onwer variant also cause rcu stall before we apply this patch set
>>>
>>> Paolo, could you help out with an (x86) KVM interface for this?
>>
>> If it's just for spin loops, you can check if the version field in the
>> steal time structure has changed.
> 
> Steal time will not be updated until ahead of next vmentry except
> wrmsr MSR_KVM_STEAL_TIME. So it can't represent it is preempted
> currently, right?

Hmm, you're right.  We can use bit 0 of struct kvm_steal_time's flags to
indicate that pad[0] is a "VCPU preempted" field; if pad[0] is 1, the
VCPU has been scheduled out since the last time the guest reset the bit.
 The guest can use an xchg to test-and-clear it.  The bit can be
accessed at any time, independent of the version field.

Paolo

Thread

[PATCH v2 0/4] implement vcpu preempted check Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-06-28 12:50 +0200
  [PATCH v2 1/4] kernel/sched: introduce vcpu preempted check interface Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-06-28 12:50 +0200
  [PATCH v2 3/4] locking/osq: Drop the overload of osq_lock() Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-06-28 12:50 +0200
  [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-06-28 12:50 +0200
    Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check Wanpeng Li <kernellwp@gmail.com> - 2016-07-05 12:00 +0200
      Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-07-06 07:00 +0200
        Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check Wanpeng Li <kernellwp@gmail.com> - 2016-07-06 08:50 +0200
          Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-07-06 10:00 +0200
            Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check Wanpeng Li <kernellwp@gmail.com> - 2016-07-06 10:40 +0200
              Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-07-06 12:20 +0200
    Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check Balbir Singh <bsingharora@gmail.com> - 2016-07-06 13:00 +0200
  [PATCH v2 4/4] kernel/locking: Drop the overload of {mutex,rwsem}_spin_on_owner Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-06-28 12:50 +0200
  Re: [PATCH v2 0/4] implement vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-07-06 09:00 +0200
    Re: [PATCH v2 0/4] implement vcpu preempted check Juergen Gross <jgross@suse.com> - 2016-07-06 09:50 +0200
      Re: [PATCH v2 0/4] implement vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-07-06 10:20 +0200
        Re: [PATCH v2 0/4] implement vcpu preempted check Juergen Gross <jgross@suse.com> - 2016-07-06 10:40 +0200
        Re: [PATCH v2 0/4] implement vcpu preempted check Paolo Bonzini <pbonzini@redhat.com> - 2016-07-06 14:50 +0200
        Re: [PATCH v2 0/4] implement vcpu preempted check Christian Borntraeger <borntraeger@de.ibm.com> - 2016-07-06 19:00 +0200
    Re: [PATCH v2 0/4] implement vcpu preempted check xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-07-06 12:10 +0200
    Re: [PATCH v2 0/4] implement vcpu preempted check Paolo Bonzini <pbonzini@redhat.com> - 2016-07-06 12:50 +0200
      Re: [PATCH v2 0/4] implement vcpu preempted check Wanpeng Li <kernellwp@gmail.com> - 2016-07-06 14:10 +0200
        Re: [PATCH v2 0/4] implement vcpu preempted check Paolo Bonzini <pbonzini@redhat.com> - 2016-07-06 14:40 +0200
          Re: [PATCH v2 0/4] implement vcpu preempted check Wanpeng Li <kernellwp@gmail.com> - 2016-07-06 15:10 +0200
          Re: [PATCH v2 0/4] implement vcpu preempted check Wanpeng Li <kernellwp@gmail.com> - 2016-07-07 10:50 +0200
            Re: [PATCH v2 0/4] implement vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-07-07 11:50 +0200
              Re: [PATCH v2 0/4] implement vcpu preempted check Wanpeng Li <kernellwp@gmail.com> - 2016-07-07 12:20 +0200
                Re: [PATCH v2 0/4] implement vcpu preempted check Wanpeng Li <kernellwp@gmail.com> - 2016-07-07 12:30 +0200
                Re: [PATCH v2 0/4] implement vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-07-07 13:20 +0200
                Re: [PATCH v2 0/4] implement vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-07-07 13:10 +0200
              Re: [PATCH v2 0/4] implement vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-07-07 13:10 +0200
              Re: [PATCH v2 0/4] implement vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-07-07 13:30 +0200
      Re: [PATCH v2 0/4] implement vcpu preempted check Peter Zijlstra <peterz@infradead.org> - 2016-07-06 14:10 +0200

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