On Sun, 2014-08-03 at 22:36 -0400, Waiman Long wrote: > 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%
So at a very low level you see nicer results, which aren't really translating to much of a significant impact at a higher level (aim7). > 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) I worry about complicating rwsems even _more_ than they are, specially for such a marginal gain. You might want to try other workloads -- ie: postgresql (pgbench), I normally get pretty useful data when dealing with rwsems. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
