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

From	Wanpeng Li <kernellwp@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 0/4] implement vcpu preempted check
Date	2016-07-07 10:50 +0200
Message-ID	<rSdap-4y2-5@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> <rRUhs-Lb-13@gated-at.bofh.it>
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2016-07-06 20:28 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> 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.

If one vCPU is preempted, and guest check it several times before this
vCPU is scheded in, then the first time we can get "vCPU is
preempted", however, since the field is cleared, the second time we
will get "vCPU is running".

Do you mean we should call record_steal_time() in both kvm_sched_in()
and kvm_sched_out() to record this field? Btw, if we should keep both
vcpu->preempted and kvm_steal_time's "vCPU preempted" field present
simultaneous?

Regards,
Wanpeng Li

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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