linux-kernel - Re: [PATCH] sched/fair: no sync wakeup from interrupt context

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Date:   Mon, 1 Aug 2022 15:26:39 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     K Prateek Nayak <kprateek.nayak@....com>
Cc:     Libo Chen <libo.chen@...cle.com>, peterz@...radead.org,
        vincent.guittot@...aro.org, mgorman@...e.de,
        tim.c.chen@...ux.intel.com, 21cnbao@...il.com,
        dietmar.eggemann@....com, linux-kernel@...r.kernel.org,
        tglx@...utronix.de
Subject: Re: [PATCH] sched/fair: no sync wakeup from interrupt context


* K Prateek Nayak <kprateek.nayak@....com> wrote:

> Hello Libo and Peter,
> 
> tl;dr
> 
> - We observed a major regression with tbench when testing the latest tip
>   sched/core at:
>   commit 14b3f2d9ee8d "sched/fair: Disallow sync wakeup from interrupt context"
>   Reason for the regression are the fewer affine wakeups that leaves the
>   client farther away from the data it needs to consume next primed in the
>   waker's LLC.
>   Such regressions can be expected from tasks that use sockets to communicate
>   significant amount of data especially on system with multiple LLCs.
> 
> - Other benchmarks have a comparable behavior to the tip at previous commit
>   commit : 91caa5ae2424 "sched/core: Fix the bug that task won't enqueue
>   into core tree when update cookie"
> 
> I'll leave more details below.

Mel Gorman also warned about this negative side-effect in:

   Subject: Re: [PATCH] sched/fair: no sync wakeup from interrupt context
   Date: Fri, 15 Jul 2022 11:07:38 +0100
   Message-ID: <20220715100738.GD3493@...e.de>

   https://lore.kernel.org/all/20220715100738.GD3493@suse.de/

I've reverted this commit (14b3f2d9ee8df3b) for the time being from 
tip:sched/core.

Thanks for the heads-up!

Thanks,

	Ingo