Messages in this thread | | | From | Joel Fernandes <> | Date | Tue, 10 Oct 2023 13:55:00 -0400 | Subject | Re: [PATCH RFC] sched/fair: Avoid unnecessary IPIs for ILB |
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On Mon, Oct 9, 2023 at 7:25 AM Ingo Molnar <mingo@kernel.org> wrote: > > > * Joel Fernandes <joel@joelfernandes.org> wrote: > > > > > Fixes: 7fd7a9e0caba ("sched/fair: Trigger nohz.next_balance updates when a CPU goes NOHZ-idle") > > > > > > Hurm.. does this really warrant a Fixes tag? Afaict nothing is currently > > > broken -- this is a pure optimization question, no? > > > > IMHO it is a breakage as it breaks NOHZ -- a lot of times the ILB kicks > > back the CPU stopping the tick out of idle (effectively breaking NOHZ). > > The large number of IPIs also wrecks power and it happens only on 6.1 and > > after. Having the fixes tag means it will also goto all stable kernels >= > > 6.1. Hope that sounds reasonable and thank you for taking a look! > > So it's basically a fix of a NOHZ performance regression, introduced by > 7fd7a9e0caba or so, correct?
Yes.
> As long as the fixes have a good hope of being backported with a low amount > of overhead, a Fixes: tag for a ~2 years old performance regression is > unusual but not unprecedented. > > We just need to make sure we don't put too much of a burden on the > shoulders of -stable maintainers ...
Sure, that sounds good. After we upstream, I am happy to assist in any stable backporting work related to this as well. In any case, I have to backport it to ChromeOS kernels which are based on stable. There's only the 6.1 stable kernel at the moment that is affected.
thanks,
- Joel
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