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authorDavidlohr Bueso <dave@stgolabs.net>2019-01-03 15:27:09 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-02-20 10:13:14 +0100
commite1d575b52c32b40184c1d1ca6039e8c7d3ce2db7 (patch)
treea579ee3c96b1daf50d8405035c3c1a6346912f88 /fs/binfmt_script.c
parent25768bb65482dd453ab7ebf8c103ec5313fd8aa5 (diff)
fs/epoll: drop ovflist branch prediction
[ Upstream commit 76699a67f3041ff4c7af6d6ee9be2bfbf1ffb671 ] The ep->ovflist is a secondary ready-list to temporarily store events that might occur when doing sproc without holding the ep->wq.lock. This accounts for every time we check for ready events and also send events back to userspace; both callbacks, particularly the latter because of copy_to_user, can account for a non-trivial time. As such, the unlikely() check to see if the pointer is being used, seems both misleading and sub-optimal. In fact, we go to an awful lot of trouble to sync both lists, and populating the ovflist is far from an uncommon scenario. For example, profiling a concurrent epoll_wait(2) benchmark, with CONFIG_PROFILE_ANNOTATED_BRANCHES shows that for a two threads a 33% incorrect rate was seen; and when incrementally increasing the number of epoll instances (which is used, for example for multiple queuing load balancing models), up to a 90% incorrect rate was seen. Similarly, by deleting the prediction, 3% throughput boost was seen across incremental threads. Link: http://lkml.kernel.org/r/20181108051006.18751-4-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Jason Baron <jbaron@akamai.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'fs/binfmt_script.c')
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