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From: Peter Zijlstra <>
To: Vincent Guittot <>
Cc: "Morotti, Romain (London)" <>,
	Ingo Molnar <>,
	Juri Lelli <>,
	"" <>
Subject: Re: kernel/scheduler: The Linux scheduler doesn't scale to more than 8 cores?
Date: Tue, 2 Nov 2021 17:04:02 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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.

      reply	other threads:[~2021-11-02 16:54 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2021-11-02 15:25 ` kernel/scheduler: The Linux scheduler doesn't scale to more than 8 cores? Vincent Guittot
2021-11-02 16:04   ` Peter Zijlstra [this message]

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