Messages in this thread | | | Date | Mon, 13 May 2019 13:35:18 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC V2 2/2] sched/fair: Fallback to sched-idle CPU if idle CPU isn't found |
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On Mon, May 13, 2019 at 03:04:18PM +0530, Viresh Kumar wrote: > On 10-05-19, 09:21, Peter Zijlstra wrote:
> > I don't hate his per se; but the whole select_idle_sibling() thing is > > something that needs looking at. > > > > There was the task stealing thing from Steve that looked interesting and > > that would render your apporach unfeasible. > > I am surely missing something as I don't see how that patchset will > make this patchset perform badly, than what it already does.
Nah; I just misremembered. I know Oracle has a patch set poking at select_idle_siblings() _somewhere_ (as do I), and I just found the wrong one.
Basically everybody is complaining select_idle_sibling() is too expensive for checking the entire LLC domain, except for FB (and thus likely some other workloads too) that depend on it to kill their tail latency.
But I suppose we could still do this, even if we scan only a subset of the LLC, just keep track of the last !idle CPU running only SCHED_IDLE tasks and pick that if you do not (in your limited scan) find a better candidate.
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