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

Florian Bezdeka
2025-04-14T08:54:56Z

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