linux-kernel - Re: Very high scheduling delay with plenty of idle CPUs

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Message-ID: <20241108083133.GD38786@noisy.programming.kicks-ass.net>
Date: Fri, 8 Nov 2024 09:31:33 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Saravana Kannan <saravanak@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Benjamin Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, wuyun.abel@...edance.com,
	youssefesmat@...omium.org, Thomas Gleixner <tglx@...utronix.de>,
	efault@....de, K Prateek Nayak <kprateek.nayak@....com>,
	John Stultz <jstultz@...gle.com>,
	Vincent Palomares <paillon@...gle.com>
Subject: Re: Very high scheduling delay with plenty of idle CPUs

On Thu, Nov 07, 2024 at 11:28:07PM -0800, Saravana Kannan wrote:
> Hi scheduler folks,
> 
> I'm running into some weird scheduling issues when testing non-sched
> changes on a Pixel 6 that's running close to 6.12-rc5. I'm not sure if
> this is an issue in earlier kernel versions or not.
> 

It's a bit unfortunate you don't have a known good kernel there. Anyway,
one thing that recently came up is that DELAY_DEQUEUE can cause some
delays, specifically it can inhibit wakeup migration.

You can either test with that feature turned off, or apply something
like the following patch:

  https://lkml.kernel.org/r/20241106135346.GL24862@noisy.programming.kicks-ass.net