linux-kernel - Re: task_non_contending() for fair

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Message-ID: <aHi8yk8wlVJBFzSR@jlelli-thinkpadt14gen4.remote.csb>
Date: Thu, 17 Jul 2025 11:05:14 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: markus.stockhausen@....de
Cc: peterz@...radead.org,
	'Chris Packham' <Chris.Packham@...iedtelesis.co.nz>, bjorn@...k.no,
	mingo@...hat.com, vincent.guittot@...aro.org,
	anna-maria@...utronix.de, frederic@...nel.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org
Subject: Re: task_non_contending() for fair_server leads to timer retries

Hi,

On 15/07/25 16:39, markus.stockhausen@....de wrote:
> Hi Peter,
> 
> I'm currently investigating issues with the timer-rtl-otto driver in 
> 6.12 longterm on the Realtek MIPS switch platform (Chris is working
> hard to upstream this). While doing so I observed that timer retries 
> continually increase (~6/second) according to /proc/timer_list. The 
> system is otherwise totally idle. 6.6 longterm does not show that issue.
> I'm unsure if this is related but documentation reads like "that's bad". 
> 
> To be sure about this one I nailed it down to the fair server.

Apologies for interjecting before Peter had a chance to reply, but I had
a first look and I wonder if this recent patch from Peter (on
tip/sched/core atm) can already help with the issue, as it should
reduce the number of dl-server dequeues:

cccb45d7c4295 ("sched/deadline: Less agressive dl_server handling")

Can you please check what you see with it?

Thanks!
Juri