linux-kernel - Re: [PATCH 2/2] sched/fair: Scale wakeup granularity relative to nr

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Message-ID: <YVwblBZ9JBn9vvVr@hirez.programming.kicks-ass.net>
Date:   Tue, 5 Oct 2021 11:32:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Mike Galbraith <efault@....de>, Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] sched/fair: Scale wakeup granularity relative to
 nr_running

On Wed, Sep 22, 2021 at 02:20:02PM +0100, Mel Gorman wrote:
> 
> Note that the TuneD throughput-performance profile allows up to 15ms
> for sysctl_sched_latency (ignoring scaling) but there is no explanation
> why such a long period was necessary or why sched_latency_ns is also
> not adjusted. The intent may have been to disable wakeup preemption
> or it might be an oversight.  An internet search for instances where
> sysctl_sched_wakeup_granularity parameter are tuned to high values offer
> either no explanation or a broken one.

FWIW, if one wants to disable wakeup preemption, we've got SCHED_BATCH
for that.