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Date: Sun, 3 Aug 2014 22:36:15 -0400 From: Waiman Long <Waiman.Long@...com> To: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org> Cc: linux-kernel@...r.kernel.org, linux-api@...r.kernel.org, linux-doc@...r.kernel.org, Davidlohr Bueso <davidlohr@...com>, Jason Low <jason.low2@...com>, Scott J Norton <scott.norton@...com>, Waiman Long <Waiman.Long@...com> Subject: [PATCH 0/7] locking/rwsem: enable reader opt-spinning & writer respin This patch set improves upon the rwsem optimistic spinning patch set from Davidlohr to enable better performing rwsem and more aggressive use of optimistic spinning. By using a microbenchmark running 1 million lock-unlock operations per thread on a 4-socket 40-core Westmere-EX x86-64 test machine running 3.16-rc7 based kernels, the following table shows the execution times with 2/10 threads running on different CPUs on the same socket where load is the number of pause instructions in the critical section: lock/r:w ratio # of threads Load:Execution Time (ms) -------------- ------------ ------------------------ mutex 2 1:530.7, 5:406.0, 10:472.7 mutex 10 1:1848 , 5:2046 , 10:4394 Before patch: rwsem/0:1 2 1:339.4, 5:368.9, 10:394.0 rwsem/1:1 2 1:2915 , 5:2621 , 10:2764 rwsem/10:1 2 1:891.2, 5:779.2, 10:827.2 rwsem/0:1 10 1:5618 , 5:5722 , 10:5683 rwsem/1:1 10 1:14562, 5:14561, 10:14770 rwsem/10:1 10 1:5914 , 5:5971 , 10:5912 After patch: rwsem/0:1 2 1:161.1, 5:244.4, 10:271.4 rwsem/1:1 2 1:188.8, 5:212.4, 10:312.9 rwsem/10:1 2 1:168.8, 5:179.5, 10:209.8 rwsem/0:1 10 1:1306 , 5:1733 , 10:1998 rwsem/1:1 10 1:1512 , 5:1602 , 10:2093 rwsem/10:1 10 1:1267 , 5:1458 , 10:2233 % Change: rwsem/0:1 2 1:-52.5%, 5:-33.7%, 10:-31.1% rwsem/1:1 2 1:-93.5%, 5:-91.9%, 10:-88.7% rwsem/10:1 2 1:-81.1%, 5:-77.0%, 10:-74.6% rwsem/0:1 10 1:-76.8%, 5:-69.7%, 10:-64.8% rwsem/1:1 10 1:-89.6%, 5:-89.0%, 10:-85.8% rwsem/10:1 10 1:-78.6%, 5:-75.6%, 10:-62.2% It can be seen that there is dramatic reduction in the execution times. The new rwsem is now even faster than mutex whether it is all writers or a mixture of writers and readers. Running the AIM7 benchmarks on the same 40-core system (HT off), the performance improvements on some of the workloads were as follows: Workload Before Patch After Patch % Change -------- ------------ ----------- -------- custom (200-1000) 446135 477404 +7.0% custom (1100-2000) 449665 484734 +7.8% high_systime 152437 154217 +1.2% (200-1000) high_systime 269695 278942 +3.4% (1100-2000) Waiman Long (7): locking/rwsem: don't resched at the end of optimistic spinning locking/rwsem: more aggressive use of optimistic spinning locking/rwsem: check for active writer/spinner before wakeup locking/rwsem: threshold limited spinning for active readers locking/rwsem: move down rwsem_down_read_failed function locking/rwsem: enables optimistic spinning for readers locking/rwsem: allow waiting writers to go back to optimistic spinning include/linux/osq_lock.h | 5 + include/linux/rwsem.h | 7 + kernel/locking/rwsem-xadd.c | 328 ++++++++++++++++++++++++++++++++++--------- kernel/locking/rwsem.c | 17 ++- 4 files changed, 288 insertions(+), 69 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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