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authorWaiman Long <Waiman.Long@hp.com>2015-07-09 19:32:22 +0300
committerIngo Molnar <mingo@kernel.org>2015-08-03 11:57:10 +0300
commitffffeaf318bd8da036eb8eb784b025a9f829201b (patch)
treeae720a4c3fbb897b1833064b0ab4bc01f113ebe3 /kernel/locking/qspinlock_paravirt.h
parent3b3fdf10a8add87ef0050138d51bfee9ab4983df (diff)
downloadlinux-ffffeaf318bd8da036eb8eb784b025a9f829201b.tar.xz
locking/qrwlock: Reduce reader/writer to reader lock transfer latency
Currently, a reader will check first to make sure that the writer mode byte is cleared before incrementing the reader count. That waiting is not really necessary. It increases the latency in the reader/writer to reader transition and reduces readers performance. This patch eliminates that waiting. It also has the side effect of reducing the chance of writer lock stealing and improving the fairness of the lock. Using a locking microbenchmark, a 10-threads 5M locking loop of mostly readers (RW ratio = 10,000:1) has the following performance numbers in a Haswell-EX box: Kernel Locking Rate (Kops/s) ------ --------------------- 4.1.1 15,063,081 4.1.1+patch 17,241,552 (+14.4%) Signed-off-by: Waiman Long <Waiman.Long@hp.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Douglas Hatch <doug.hatch@hp.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Scott J Norton <scott.norton@hp.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Link: http://lkml.kernel.org/r/1436459543-29126-2-git-send-email-Waiman.Long@hp.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking/qspinlock_paravirt.h')
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