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Re: [PATCH 1/2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function

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On Wed, Feb 08, 2017 at 01:00:24PM -0500, Waiman Long wrote:
> It was found when running fio sequential write test with a XFS ramdisk
> on a 2-socket x86-64 system, the %CPU times as reported by perf were
> as follows:
> 
>  71.27%  0.28%  fio  [k] down_write
>  70.99%  0.01%  fio  [k] call_rwsem_down_write_failed
>  69.43%  1.18%  fio  [k] rwsem_down_write_failed
>  65.51% 54.57%  fio  [k] osq_lock
>   9.72%  7.99%  fio  [k] __raw_callee_save___kvm_vcpu_is_preempted
>   4.16%  4.16%  fio  [k] __kvm_vcpu_is_preempted
> 
> So making vcpu_is_preempted() a callee-save function has a pretty high
> cost associated with it. As vcpu_is_preempted() is called within the
> spinlock, mutex and rwsem slowpaths, there isn't much to gain by making
> it callee-save. So it is now changed to a normal function call instead.
> 

Numbers for bare metal too please.

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[PATCH 1/2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function Waiman Long <longman@redhat.com> - 2017-02-08 19:10 +0100
  [PATCH 2/2] locking/mutex,rwsem: Reduce vcpu_is_preempted() calling frequency Waiman Long <longman@redhat.com> - 2017-02-08 19:10 +0100
    Re: [PATCH 2/2] locking/mutex,rwsem: Reduce vcpu_is_preempted()  calling frequency Waiman Long <longman@redhat.com> - 2017-02-08 20:20 +0100
    Re: [PATCH 2/2] locking/mutex,rwsem: Reduce vcpu_is_preempted()  calling frequency Peter Zijlstra <peterz@infradead.org> - 2017-02-08 21:00 +0100
  Re: [PATCH 1/2] x86/paravirt: Don't make vcpu_is_preempted() a  callee-save function Peter Zijlstra <peterz@infradead.org> - 2017-02-08 20:20 +0100
    Re: [PATCH 1/2] x86/paravirt: Don't make vcpu_is_preempted() a  callee-save function Waiman Long <longman@redhat.com> - 2017-02-08 21:50 +0100

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