Re: [PATCH v5 0/6] rwsem: performance optimizations

From: Davidlohr Bueso
Date: Tue Sep 24 2013 - 23:32:24 EST

On Tue, 2013-09-24 at 15:22 -0700, Tim Chen wrote:
> We have incorporated various suggestions from Ingo for version 5 of this patchset
> and will like to have it merged if there are no objections.
> In this patchset, we introduce two categories of optimizations to read
> write semaphore. The first four patches from Alex Shi reduce cache bouncing of the
> sem->count field by doing a pre-read of the sem->count and avoid cmpxchg
> if possible.
> The last two patches introduce similar optimistic spinning logic as
> the mutex code for the writer lock acquisition of rwsem.

Right. We address the general 'mutexes out perform writer-rwsems'
situations that has been seen in more than one case. Users now need not
worry about performance issues when choosing between these two locking


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