| Message ID | 20181212110357.25656-1-rpenyaev@suse.de (mailing list archive) |
|---|---|
| Headers | show |
| Series | use rwlock in order to reduce ep_poll_callback() contention | expand |
On 2018-12-12 03:03, Roman Penyaev wrote: > The last patch targets the contention problem in ep_poll_callback(), > which > can be very well reproduced by generating events (write to pipe or > eventfd) > from many threads, while consumer thread does polling. > > The following are some microbenchmark results based on the test [1] > which > starts threads which generate N events each. The test ends when all > events > are successfully fetched by the poller thread: > > spinlock > ======== > > threads events/ms run-time ms > 8 6402 12495 > 16 7045 22709 > 32 7395 43268 > > rwlock + xchg > ============= > > threads events/ms run-time ms > 8 10038 7969 > 16 12178 13138 > 32 13223 24199 > > > According to the results bandwidth of delivered events is significantly > increased, thus execution time is reduced. > > This series is based on linux-next/akpm and differs from RFC in that > additional cleanup patches and explicit comments have been added. > > [1] https://github.com/rouming/test-tools/blob/master/stress-epoll.c Care to "port" this to 'perf bench epoll', in linux-next? I've been trying to unify into perf bench the whole epoll performance testcases kernel developers can use when making changes and it would be useful. I ran these patches on the 'wait' workload which is a epoll_wait(2) stresser. On a 40-core IvyBridge it shows good performance improvements for increasing number of file descriptors each of the 40 threads deals with: 64 fds: +20% 512 fds: +30% 1024 fds: +50% (Yes these are pretty raw measurements ops/sec). Unlike your benchmark, though, there is only single writer thread, and therefore is less ideal to measure optimizations when IO becomes available. Hence it would be nice to also have this. Thanks, Davidlohr
On 2018-12-13 19:13, Davidlohr Bueso wrote: > On 2018-12-12 03:03, Roman Penyaev wrote: >> The last patch targets the contention problem in ep_poll_callback(), >> which >> can be very well reproduced by generating events (write to pipe or >> eventfd) >> from many threads, while consumer thread does polling. >> >> The following are some microbenchmark results based on the test [1] >> which >> starts threads which generate N events each. The test ends when all >> events >> are successfully fetched by the poller thread: >> >> spinlock >> ======== >> >> threads events/ms run-time ms >> 8 6402 12495 >> 16 7045 22709 >> 32 7395 43268 >> >> rwlock + xchg >> ============= >> >> threads events/ms run-time ms >> 8 10038 7969 >> 16 12178 13138 >> 32 13223 24199 >> >> >> According to the results bandwidth of delivered events is >> significantly >> increased, thus execution time is reduced. >> >> This series is based on linux-next/akpm and differs from RFC in that >> additional cleanup patches and explicit comments have been added. >> >> [1] https://github.com/rouming/test-tools/blob/master/stress-epoll.c > > Care to "port" this to 'perf bench epoll', in linux-next? I've been > trying to unify into perf bench the whole epoll performance testcases > kernel developers can use when making changes and it would be useful. Yes, good idea. But frankly I do not want to bloat epoll-wait.c with my multi-writers-single-reader test case, because soon epoll-wait.c will become unmaintainable with all possible loads and set of different options. Can we have a single, small and separate source for each epoll load? Easy to fix, easy to maintain, debug/hack. > I ran these patches on the 'wait' workload which is a epoll_wait(2) > stresser. On a 40-core IvyBridge it shows good performance > improvements for increasing number of file descriptors each of the 40 > threads deals with: > > 64 fds: +20% > 512 fds: +30% > 1024 fds: +50% > > (Yes these are pretty raw measurements ops/sec). Unlike your > benchmark, though, there is only single writer thread, and therefore > is less ideal to measure optimizations when IO becomes available. > Hence it would be nice to also have this. That's weird. One writer thread does not content with anybody, only with consumers, so should not be any big difference. -- Roman
On 2018-12-17 03:49, Roman Penyaev wrote: > On 2018-12-13 19:13, Davidlohr Bueso wrote: > Yes, good idea. But frankly I do not want to bloat epoll-wait.c with > my multi-writers-single-reader test case, because soon epoll-wait.c > will become unmaintainable with all possible loads and set of > different options. > > Can we have a single, small and separate source for each epoll load? > Easy to fix, easy to maintain, debug/hack. Yes completely agree; I was actually thinking along those lines. > >> I ran these patches on the 'wait' workload which is a epoll_wait(2) >> stresser. On a 40-core IvyBridge it shows good performance >> improvements for increasing number of file descriptors each of the 40 >> threads deals with: >> >> 64 fds: +20% >> 512 fds: +30% >> 1024 fds: +50% >> >> (Yes these are pretty raw measurements ops/sec). Unlike your >> benchmark, though, there is only single writer thread, and therefore >> is less ideal to measure optimizations when IO becomes available. >> Hence it would be nice to also have this. > > That's weird. One writer thread does not content with anybody, only > with > consumers, so should not be any big difference. Yeah so the irq optimization patch, which is known to boost numbers on this microbench, plays an important factor. I just put them all together when testing. Thanks, Davidlohr
The last patch targets the contention problem in ep_poll_callback(), which can be very well reproduced by generating events (write to pipe or eventfd) from many threads, while consumer thread does polling. The following are some microbenchmark results based on the test [1] which starts threads which generate N events each. The test ends when all events are successfully fetched by the poller thread: spinlock ======== threads events/ms run-time ms 8 6402 12495 16 7045 22709 32 7395 43268 rwlock + xchg ============= threads events/ms run-time ms 8 10038 7969 16 12178 13138 32 13223 24199 According to the results bandwidth of delivered events is significantly increased, thus execution time is reduced. This series is based on linux-next/akpm and differs from RFC in that additional cleanup patches and explicit comments have been added. [1] https://github.com/rouming/test-tools/blob/master/stress-epoll.c Roman Penyaev (3): epoll: make sure all elements in ready list are in FIFO order epoll: loosen irq safety in ep_poll_callback() epoll: use rwlock in order to reduce ep_poll_callback() contention fs/eventpoll.c | 127 ++++++++++++++++++++++++++++++++++++------------- 1 file changed, 93 insertions(+), 34 deletions(-) Signed-off-by: Roman Penyaev <rpenyaev@suse.de> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: Jason Baron <jbaron@akamai.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org