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

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On 06/03/2016 05:48 AM, 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.
>
> Signed-off-by: Pan Xinhui<xinhui.pan@linux.vnet.ibm.com>
> ---
>   kernel/locking/qspinlock.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
> index 99f31e4..2b4daac 100644
> --- a/kernel/locking/qspinlock.c
> +++ b/kernel/locking/qspinlock.c
> @@ -492,7 +492,7 @@ release:
>   	/*
>   	 * release the node
>   	 */
> -	this_cpu_dec(mcs_nodes[0].count);
> +	this_cpu_ptr(&mcs_nodes[0])->count--;
>   }
>   EXPORT_SYMBOL(queued_spin_lock_slowpath);
>

Is this going to generate better code for PPC? For x86, I think it will 
cause more instruction to be issued.

Cheers,
Longman

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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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