linux-kernel - Re: [PATCH v3 3/5] sched/fair: Switch to task based throttle model

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Message-ID: <91b75418-c836-4098-9f7e-4b287598a1d7@amd.com>
Date: Thu, 4 Sep 2025 13:56:38 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: "Bezdeka, Florian" <florian.bezdeka@...mens.com>, "ziqianlu@...edance.com"
	<ziqianlu@...edance.com>
CC: "liusongtang@...edance.com" <liusongtang@...edance.com>,
	"dietmar.eggemann@....com" <dietmar.eggemann@....com>,
	"zhouchuyi@...edance.com" <zhouchuyi@...edance.com>, "bigeasy@...utronix.de"
	<bigeasy@...utronix.de>, "mgorman@...e.de" <mgorman@...e.de>, "Kiszka, Jan"
	<jan.kiszka@...mens.com>, "vincent.guittot@...aro.org"
	<vincent.guittot@...aro.org>, "chengming.zhou@...ux.dev"
	<chengming.zhou@...ux.dev>, "mingo@...hat.com" <mingo@...hat.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>, "joshdon@...gle.com"
	<joshdon@...gle.com>, "vschneid@...hat.com" <vschneid@...hat.com>,
	"xii@...gle.com" <xii@...gle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "peterz@...radead.org"
	<peterz@...radead.org>, "bsegall@...gle.com" <bsegall@...gle.com>,
	"juri.lelli@...hat.com" <juri.lelli@...hat.com>
Subject: Re: [PATCH v3 3/5] sched/fair: Switch to task based throttle model

Hello Florian,

On 9/4/2025 1:03 PM, Bezdeka, Florian wrote:
> Hi Aaron,
> 
> On Wed, 2025-09-03 at 19:35 +0800, Aaron Lu wrote:
>>
>>> [..snip..]
>>>>
>>
>> Just want to add that with the above diff applied, I also tested
>> songtang's stress test[0] and Jan's rt deadlock reproducer[1] and didn't
>> see any problem.
> 
> Thanks a lot for taking the reproducer into account. But: To trigger
> PREEMPT_RT needs to be enabled, otherwise the rwlock in the epoll
> infrastructure (that we highly stress) won't sleep. Just to be sure:
> PREEMPT_RT was enabled on your end?

I've too tested this series with Jan's reproducer on PREEMPT_RT and
can confirm no hang was triggered over a full weekend run lasting
more than 72Hrs with Aaron's changes applied on top of v6.16-rc6
based kernel.

> 
>>
>> [0]: https://lore.kernel.org/lkml/20250715072218.GA304@bytedance/
>> [1]: https://lore.kernel.org/all/7483d3ae-5846-4067-b9f7-390a614ba408@siemens.com/

I used the same reproducer from [1] with small modification to
run.sh to periodically move epoll-stall and epoll-stall-writer
to one particular CPU and keep changing this CPU ever minute. 

-- 
Thanks and Regards,
Prateek