linux-kernel - Re: [RFC PATCH v2 0/7] Defer throttle when task exits to user

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Message-ID: <20250414120407.GC3558904@bytedance>
Date: Mon, 14 Apr 2025 20:04:07 +0800
From: Aaron Lu <ziqianlu@...edance.com>
To: Florian Bezdeka <florian.bezdeka@...mens.com>
Cc: Valentin Schneider <vschneid@...hat.com>,
	Ben Segall <bsegall@...gle.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Don <joshdon@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Xi Wang <xii@...gle.com>, linux-kernel@...r.kernel.org,
	Juri Lelli <juri.lelli@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>, Mel Gorman <mgorman@...e.de>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Chuyi Zhou <zhouchuyi@...edance.com>,
	Jan Kiszka <jan.kiszka@...mens.com>
Subject: Re: [RFC PATCH v2 0/7] Defer throttle when task exits to user

Hi Florian,

On Mon, Apr 14, 2025 at 10:54:48AM +0200, Florian Bezdeka wrote:
> Hi Aaron, Hi Valentin,
> 
> On Wed, 2025-04-09 at 20:07 +0800, Aaron Lu wrote:
> > This is a continuous work based on Valentin Schneider's posting here:
> > Subject: [RFC PATCH v3 00/10] sched/fair: Defer CFS throttle to user entry
> > https://lore.kernel.org/lkml/20240711130004.2157737-1-vschneid@redhat.com/
> > 
> > Valentin has described the problem very well in the above link. We also
> > have task hung problem from time to time in our environment due to cfs quota.
> > It is mostly visible with rwsem: when a reader is throttled, writer comes in
> > and has to wait, the writer also makes all subsequent readers wait,
> > causing problems of priority inversion or even whole system hung.
> 
> for testing purposes I backported this series to 6.14. We're currently
> hunting for a sporadic bug with PREEMPT_RT enabled. We see RCU stalls
> and complete system freezes after a couple of days with some container
> workload deployed. See [1]. 

I tried to make a setup last week to reproduce the RT/cfs throttle
deadlock issue Valentin described but haven't succeeded yet...

> It's too early to report "success", but this series seems to fix the
> circular dependency / system hang. Testing is still ongoing.

Good to know this and thanks for giving it a try.

> While backporting I noticed some minor code style "issues". I will post
> them afterwards. Feel free to ignore...

Your comments are welcome.

Best regards,
Aaron

> 
> [1] https://lore.kernel.org/linux-rt-users/20250409135720.YuroItHp@linutronix.de/T/#t