Messages in this thread | | | Date | Tue, 2 Nov 2021 17:04:02 +0100 | From | Peter Zijlstra <> | Subject | Re: kernel/scheduler: The Linux scheduler doesn't scale to more than 8 cores? |
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On Tue, Nov 02, 2021 at 04:25:05PM +0100, Vincent Guittot wrote: > > From the first line, the CPU count is capped to 8. > > > > Thus the scheduler scaling won't be more than a factor of 4, no matter how many CPUs there are. (1+log2(8)) > > > > There's also a linear scaling option, that is similarly capped to 8 times, because 8 CPUs. > > That's a good point and I never realized this limitation in the scaling factor. > > Peter mentioned that there were interactivity problems with large > scale factors at the time it was added. But the scheduler has changed > since and it would be interesting to run benchmarks on more recent > platforms with larger factor
The important note here is that this limit is about timescales, not anything else. Previously a 64 cpu system would blow up the latency to 6ms * (1 + ln)2(64)) = 42ms, which is atrocious.
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