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Re: [PATCH] locking/qspinlock: Use this_cpu_ptr instead of this_cpu_dec

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On 2016年06月03日 19:37, Peter Zijlstra wrote:
> On Fri, Jun 03, 2016 at 05:48:50PM +0800, Pan Xinhui wrote:
>> queued_spin_lock_slowpath should not worry about interrupt change
>> node->count by accident because ->count is inc and dec when we
>> enter/leave queued_spin_lock_slowpath.
>>
>> So this_cpu_dec() does some no point things here, lets use this_cpu_ptr
>> for a small optimization.
>
> Uhm, have you actually looked at what that does on x86?
>
yep, just one instruction inc/dec.

well, with my patch, there are two instructions.

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[PATCH] locking/qspinlock: Use this_cpu_ptr instead of this_cpu_dec Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-06-03 11:50 +0200
  Re: [PATCH] locking/qspinlock: Use this_cpu_ptr instead of  this_cpu_dec Peter Zijlstra <peterz@infradead.org> - 2016-06-03 13:40 +0200
    Re: [PATCH] locking/qspinlock: Use this_cpu_ptr instead of this_cpu_dec xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-06-06 05:30 +0200
  Re: [PATCH] locking/qspinlock: Use this_cpu_ptr instead of this_cpu_dec Waiman Long <waiman.long@hpe.com> - 2016-06-03 23:30 +0200
    Re: [PATCH] locking/qspinlock: Use this_cpu_ptr instead of  this_cpu_dec Peter Zijlstra <peterz@infradead.org> - 2016-06-03 23:40 +0200
      Re: [PATCH] locking/qspinlock: Use this_cpu_ptr instead of this_cpu_dec xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-06-06 06:50 +0200

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