From: Linus Torvalds <torvalds@linux-foundation.org> To: kernel test robot <oliver.sang@intel.com> Cc: Sandeep Patil <sspatil@android.com>, Mel Gorman <mgorman@techsingularity.net>, LKML <linux-kernel@vger.kernel.org>, lkp@lists.01.org, kernel test robot <lkp@intel.com>, "Huang, Ying" <ying.huang@intel.com>, Feng Tang <feng.tang@intel.com>, Zhengjun Xing <zhengjun.xing@linux.intel.com> Subject: Re: [pipe] 3b844826b6: stress-ng.sigio.ops_per_sec -99.3% regression Date: Tue, 24 Aug 2021 09:22:25 -0700 [thread overview] Message-ID: <CAHk-=wjEdeNW8bPNhwRCkMu6zLKjE2vQ=WL_6bQtc9YnaKt0bw@mail.gmail.com> (raw) In-Reply-To: <20210824151337.GC27667@xsang-OptiPlex-9020> On Tue, Aug 24, 2021 at 7:56 AM kernel test robot <oliver.sang@intel.com> wrote: > > FYI, we noticed a -99.3% regression of stress-ng.sigio.ops_per_sec due to commit: Well, that's bad. > commit: 3b844826b6c6 ("pipe: avoid unnecessary EPOLLET wakeups under normal loads") You fix one benchmark, you break another.. What's a bit odd is that this commit basically reverts commit 3a34b13a88ca ("pipe: make pipe writes always wake up readers") which did *not* result in any kernel test robot report. It's not a pure revert, because it adds that 'poll_usage' case (for EPOLLET), but the stress-ng.sigio test doesn't even use select or poll (ok, there's a select() call with an empty file descriptor set, which seems to be just an odd way to spell "usleep()"). So it _looks_ to me like it's a 100% revert in practice for that test. I strace'd the "stress-ng --sigio" case just to make sure I didn't miss anything. But I'm clearly missing something. Can anybody see what I'm missing, and hit me over the head with the clue-bat? Linus
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From: Linus Torvalds <torvalds@linux-foundation.org> To: lkp@lists.01.org Subject: Re: [pipe] 3b844826b6: stress-ng.sigio.ops_per_sec -99.3% regression Date: Tue, 24 Aug 2021 09:22:25 -0700 [thread overview] Message-ID: <CAHk-=wjEdeNW8bPNhwRCkMu6zLKjE2vQ=WL_6bQtc9YnaKt0bw@mail.gmail.com> (raw) In-Reply-To: <20210824151337.GC27667@xsang-OptiPlex-9020> [-- Attachment #1: Type: text/plain, Size: 1081 bytes --] On Tue, Aug 24, 2021 at 7:56 AM kernel test robot <oliver.sang@intel.com> wrote: > > FYI, we noticed a -99.3% regression of stress-ng.sigio.ops_per_sec due to commit: Well, that's bad. > commit: 3b844826b6c6 ("pipe: avoid unnecessary EPOLLET wakeups under normal loads") You fix one benchmark, you break another.. What's a bit odd is that this commit basically reverts commit 3a34b13a88ca ("pipe: make pipe writes always wake up readers") which did *not* result in any kernel test robot report. It's not a pure revert, because it adds that 'poll_usage' case (for EPOLLET), but the stress-ng.sigio test doesn't even use select or poll (ok, there's a select() call with an empty file descriptor set, which seems to be just an odd way to spell "usleep()"). So it _looks_ to me like it's a 100% revert in practice for that test. I strace'd the "stress-ng --sigio" case just to make sure I didn't miss anything. But I'm clearly missing something. Can anybody see what I'm missing, and hit me over the head with the clue-bat? Linus
next prev parent reply other threads:[~2021-08-24 16:22 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-08-24 15:13 [pipe] 3b844826b6: stress-ng.sigio.ops_per_sec -99.3% regression kernel test robot 2021-08-24 15:13 ` kernel test robot 2021-08-24 16:22 ` Linus Torvalds [this message] 2021-08-24 16:22 ` Linus Torvalds 2021-08-24 17:32 ` Linus Torvalds 2021-08-24 17:32 ` Linus Torvalds 2021-08-24 17:39 ` Linus Torvalds 2021-08-24 17:39 ` Linus Torvalds 2021-08-25 8:50 ` Oliver Sang 2021-08-25 8:50 ` Oliver Sang 2021-08-25 14:11 ` Eric W. Biederman 2021-08-25 14:11 ` Eric W. Biederman 2021-08-25 17:25 ` Linus Torvalds 2021-08-25 17:25 ` Linus Torvalds 2021-08-24 18:42 ` Colin Ian King 2021-08-24 18:42 ` Colin Ian King 2021-08-24 20:57 ` Colin Ian King 2021-08-24 20:57 ` Colin Ian King
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