Messages in this thread | | | Subject | Re: [PATCH v3] locking/rwsem: Avoid double checking before try acquiring write lock | From | Davidlohr Bueso <> | Date | Wed, 17 Sep 2014 11:34:37 +0200 |
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On Tue, 2014-09-16 at 17:16 -0700, Jason Low wrote: > Commit 9b0fc9c09f1b 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.
Ah, I remember you had this one in your queue for some time :)
> 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().
heh, so people don't try to remove the "redundant" check!
> Cc: Peter Hurley <peter@hurleysoftware.com> > Cc: Tim Chen <tim.c.chen@linux.intel.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
> Signed-off-by: Jason Low <jason.low2@hp.com>
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