Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: Performance regression: thread wakeup time (latency) increased up to 3x | Date | Fri, 22 Oct 2021 15:03:40 +0200 |
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On Monday, October 18, 2021 1:25:02 PM CEST Peter Zijlstra wrote: > On Fri, Oct 15, 2021 at 09:08:58PM -0700, Norbert wrote: > > > > > > On Fri, Oct 15, 2021 at 12:43:45AM -0700, Norbert wrote: > > > > > > Performance regression: thread wakeup time (latency) increased up to 3x. > > > > > > > > > > > > Happened between 5.13.8 and 5.14.0. Still happening at least on 5.14.11. > > > So git-bisect finally identified the following commit. > > The performance difference came in a single step. Times were consistent with > > my first post either the slow time or the fast time, > > as far as I could tell during the bisection. > > > > It is a bit unfortunate that this comes from an attempt to reduce OS noise. > > > > ----------------------------------------------------- > > commit a5183862e76fdc25f36b39c2489b816a5c66e2e5 > > Author: Yunfeng Ye <yeyunfeng@huawei.com> > > Date: Thu May 13 01:29:16 2021 +0200 > > > > tick/nohz: Conditionally restart tick on idle exit > > > > In nohz_full mode, switching from idle to a task will unconditionally > > issue a tick restart. If the task is alone in the runqueue or is the > > highest priority, the tick will fire once then eventually stop. But that > > alone is still undesired noise. > > > > Therefore, only restart the tick on idle exit when it's strictly > > necessary. > > > > Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com> > > Signed-off-by: Frederic Weisbecker <frederic@kernel.org> > > Signed-off-by: Ingo Molnar <mingo@kernel.org> > > Acked-by: Peter Zijlstra <peterz@infradead.org> > > Link: > > https://lore.kernel.org/r/20210512232924.150322-3-frederic@kernel.org > > ----------------------------------------------------- > > > > Is there anything else to do to complete this report? > > So it _could_ be you're seeing increased use of deeper idle states due > to less noise. I'm forever forgetting what the most friendly tool is for > checking that (powertop can I think), Rafael?
You can use turbostat too.
> One thing to try is boot with idle=halt and see if that makes a > different. > > Also, let me Cc all the people involved.. the thread starts: > > https://lkml.kernel.org/r/035c23b4-118e-6a35-36d9-1b11e3d679f8@gmail.com >
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