Messages in this thread | | | Date | Mon, 18 Oct 2021 13:25:02 +0200 | From | Peter Zijlstra <> | Subject | Re: Performance regression: thread wakeup time (latency) increased up to 3x |
| |
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?
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
| |