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Re: [RFC][PATCH] mutex: Optimize mutex_trylock() fast-path

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On Wed, 01 Jun 2016, Peter Zijlstra wrote:

>
>A while back Viro posted a number of 'interesting' mutex_is_locked()
>users on IRC, one of those was RCU.
>
>RCU seems to use mutex_is_locked() to avoid doing mutex_trylock(), the
>regular load before modify pattern.
>
>While the use isn't wrong per se, its curious in that its needed at all,
>mutex_trylock() should be good enough on its own to avoid the pointless
>cacheline bounces.

Yeah, and we use ccas just about everywhere else for mutexes.

>
>So fix those and remove the mutex_is_locked() (ab)use from RCU.
>
>Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
>Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Acked-by: Davidlohr Bueso <dave@stgolabs.net>

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[RFC][PATCH] mutex: Optimize mutex_trylock() fast-path Peter Zijlstra <peterz@infradead.org> - 2016-06-01 21:00 +0200
  Re: [RFC][PATCH] mutex: Optimize mutex_trylock() fast-path Davidlohr Bueso <dave@stgolabs.net> - 2016-06-02 16:30 +0200
  Re: [RFC][PATCH] mutex: Optimize mutex_trylock() fast-path "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-02 17:10 +0200
  [tip:locking/core] locking/mutex: Optimize mutex_trylock()  fast-path tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2016-06-08 16:30 +0200

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