Messages in this thread | | | Date | Wed, 9 Jun 2021 09:26:00 +0200 (CEST) | From | Julia Lawall <> | Subject | Re: find_new_ilb |
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On Wed, 9 Jun 2021, Peter Zijlstra wrote:
> On Tue, Jun 08, 2021 at 09:51:30PM +0200, Julia Lawall wrote: > > Starting from the following commit: > > > > commit 45da7a2b0af8fa29dff2e6ba8926322068350fce > > Author: Peter Zijlstra <peterz@infradead.org> > > Date: Tue Aug 18 10:48:17 2020 +0200 > > > > sched/fair: Exclude the current CPU from find_new_ilb() > > > > up through Linux 5.12, I observed that often when most of the machine was > > idle, there could be many (thousands) of sched_wake_idle_without_ipi > > events, typically between cores 0 and 1. I don't see this any more in > > Linux v5.13-rc1. I looked through the patches to fair.c and core.c > > subsequent to v5.12, and I didn't see anything that explicitly addresses > > this issue. Before I plunge into another set of rounds of bisecting, I > > wonder if anyone knows whether and how this problem was resolved? > > Hurmph.. that patch was preparation for a later change that never seems > to have happened. If it is causing trouble for you, I think you can > savely revert it. > > At the time I thought it was very strange that new_idle would select > itself as idle-balancer, doubly so, because the only way to get there > would be with NEED_RESCHED already set, so the IPI wouldn't in fact do > anything. > > Looking again, the difference is ofcourse that previously we'd select > self and NO-OP, but now we'll potentially select another CPU and > actually do something. > > This is arguably an improvement, because we did want to do something. > > I can't quite remember what would've change here since, Vincent, can > you remember? > > Anyway, is this actually causing you trouble, or are you just going on > the increased number of events?
Thanks for the feedback. The scenarios I saw wouldn't have caused trouble for anyone, because the machine was highly idle (maybe a couple of cores in use). And the problem seems to be gone as well in v5.13.
julia
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