On 10/11/2017 04:50 PM, Dave Chinner wrote: > On Wed, Oct 11, 2017 at 02:01:51PM -0400, Waiman Long wrote: >> In term of rwsem performance, a rwsem microbenchmark and fio randrw >> test with a xfs filesystem on a ramdisk were used to verify the >> performance changes due to these patches. Both tests were run on a >> 2-socket, 40-core Gold 6148 system. The rwsem microbenchmark (1:1 >> reader/writer ratio) has short critical section while the fio randrw >> test has long critical section (4k read/write). >> >> The following table shows the performance of the rwsem microbenchmark >> and fio radrw test with different number of patches applied on 4.14 >> based kernels: >> >> # of Patches Locking Rate FIO Bandwidth FIO Bandwidth >> Applied 40 threads 32 threads 16 threads >> ------------ ------------ ------------- ------------- >> 0 38.7 kop/s 706 MB/s 704 MB/s >> 7 38.6 kop/s 668 MB/s 663 MB/s >> 8 38.9 kop/s 704 MB/s 701 MB/s >> 9 39.1 kop/s 702 MB/s 707 MB/s >> 11 3218.0 kop/s 2594 MB/s 2614 MB/s >> >> So this patchset improves mixed read/write rwsem microbench by 83X >> and randrw fio bandwidth by about 3.7X. > Overall improvement in bandwidth is not necessarily a good thing - > this could simply demonstrate total write bandwidth starvation and > so it's only reporting read bandwith. It's much more important to > look at the change in read bandwidth vs write bandwidth in the fio > test. i.e. exactly how did the IO balance change as a result of > changing the locking bias?
Thanks for the input. I can take out the reader lock stealing part. That will give it a more fair reader/writer bias. It can also be an option that be set when the rwsem is inited. Cheers, Longman
