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authorJason Low <jason.low2@hp.com>2014-09-16 17:16:57 -0700
committerIngo Molnar <mingo@kernel.org>2014-10-03 06:09:29 +0200
commitdebfab74e453f079cd8b12b0604387a8c510ef3a (patch)
treebab0d5cc8f56dde5ad91d409683aac5d7fec8b47 /lib
parentdb0e716a1512179e8374a74c1f3184e9ce15d138 (diff)
locking/rwsem: Avoid double checking before try acquiring write lock
Commit 9b0fc9c09f1b ("rwsem: skip initial trylock in rwsem_down_write_failed") checks for if there are known active lockers in order to avoid write trylocking using expensive cmpxchg() when it likely wouldn't get the lock. However, a subsequent patch was added such that we directly check for sem->count == RWSEM_WAITING_BIAS right before trying that cmpxchg(). Thus, commit 9b0fc9c09f1b now just adds overhead. This patch modifies it so that we only do a check for if count == RWSEM_WAITING_BIAS. Also, add a comment on why we do an "extra check" of count before the cmpxchg(). Signed-off-by: Jason Low <jason.low2@hp.com> Acked-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Aswin Chandramouleeswaran <aswin@hp.com> Cc: Chegu Vinod <chegu_vinod@hp.com> Cc: Peter Hurley <peter@hurleysoftware.com> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1410913017.2447.22.camel@j-VirtualBox Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'lib')
0 files changed, 0 insertions, 0 deletions

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