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

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Message-ID: <cee5bca4e2b024d3406b40b84c0d5db91c7d276f.camel@siemens.com>
Date: Mon, 14 Apr 2025 10:54:48 +0200
From: Florian Bezdeka <florian.bezdeka@...mens.com>
To: Aaron Lu <ziqianlu@...edance.com>, 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>
Cc: 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 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]. 

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

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

Best regards,
Florian

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