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Re: [PATCH] mutex: Do not spin/queue before performing ww_mutex deadlock avoidance

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Op 26-05-16 om 12:43 schreef Chris Wilson:
> On Thu, May 26, 2016 at 12:37:30PM +0200, Maarten Lankhorst wrote:
>> The check should also not be for NULL, but for use_ww_ctx.
>> This way the if check is optimized out for the ww_ctx path, where
>> ww_ctx is always non-null.
> The compiler can see use_ww_ctx == false => ww_ctx == NULL just as well
> to do dead-code elimination, i.e. use_ww_ctx is superflouus and does not
> reduce the code size. (gcc 4.7.2, 4.9.1, 5.3.1)
That's true, but it cannot do the same when use_ww_ctx = true.
In this case the function will always be called with ww_ctx != NULL,
but the compiler can't see that, so it will keep the check even if it's always true.

~Maarten

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[PATCH] mutex: Do not spin/queue before performing ww_mutex deadlock avoidance Chris Wilson <chris@chris-wilson.co.uk> - 2016-05-26 10:40 +0200
  Re: [PATCH] mutex: Do not spin/queue before performing ww_mutex  deadlock avoidance Maarten Lankhorst <maarten.lankhorst@linux.intel.com> - 2016-05-26 12:40 +0200
    Re: [PATCH] mutex: Do not spin/queue before performing ww_mutex  deadlock avoidance Chris Wilson <chris@chris-wilson.co.uk> - 2016-05-26 12:50 +0200
      Re: [PATCH] mutex: Do not spin/queue before performing ww_mutex  deadlock avoidance Maarten Lankhorst <maarten.lankhorst@linux.intel.com> - 2016-05-26 13:10 +0200
  [PATCH] mutex: Report recursive ww_mutex locking early Chris Wilson <chris@chris-wilson.co.uk> - 2016-05-26 22:10 +0200
    Re: [PATCH] mutex: Report recursive ww_mutex locking early Maarten Lankhorst <maarten.lankhorst@linux.intel.com> - 2016-05-30 09:50 +0200
      Re: [PATCH] mutex: Report recursive ww_mutex locking early Peter Zijlstra <peterz@infradead.org> - 2016-05-30 11:20 +0200
        Re: [PATCH] mutex: Report recursive ww_mutex locking early Maarten Lankhorst <maarten.lankhorst@linux.intel.com> - 2016-05-30 11:50 +0200
          Re: [PATCH] mutex: Report recursive ww_mutex locking early Peter Zijlstra <peterz@infradead.org> - 2016-05-30 12:30 +0200
            Re: [PATCH] mutex: Report recursive ww_mutex locking early Chris Wilson <chris@chris-wilson.co.uk> - 2016-05-30 12:50 +0200
              Re: [PATCH] mutex: Report recursive ww_mutex locking early Maarten Lankhorst <maarten.lankhorst@linux.intel.com> - 2016-05-30 13:20 +0200

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