Messages in this thread | | | Date | Tue, 5 Oct 2021 10:12:12 -0400 | From | Phil Auld <> | Subject | Re: [PATCH 2/2] sched/fair: Scale wakeup granularity relative to nr_running |
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On Tue, Oct 05, 2021 at 12:36:22PM +0200 Peter Zijlstra wrote: > On Thu, Sep 23, 2021 at 08:24:03AM -0400, Phil Auld wrote: > > > It's capped at 8 cpus, which is pretty easy to reach these days, so the > > values don't get too large. That scaling is almost a no-op these days. > > https://lkml.kernel.org/r/YVwdrh5pg0zSv2/b@hirez.programming.kicks-ass.net > > Ooh, hey, we already fixed that :-) >
Thanks Peter.
I'm always a little behind upstream (nature of the job :)
That link leads to a message Id not found. But from what I can see the code that takes the min of online cpus and 8 is still present.
> So the reasoning there is that if the values get too big, interactiviy > get *really* bad, but if you go from say 1 to 4 CPUs, interactivity can > improve due to being able to run on other CPUs. > > At 8 CPUs we end up at 6ms*4=24ms, which is already pretty terrible. >
And actually you mention the same thing later on. Most systems, even desktops, have 8+ cpus these days so the scaling is mostly not doing anything except multiplying by 4, right? So no-op was not the right way to describe it maybe. But it's not getting bigger with larger numbers of cpus beyond a pretty commonly reached limit.
Cheers, Phil
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