linux-kernel - Re: [PATCH 1/4] sched/fair: Propagate load for throttled cfs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20250929075158.GA426@bytedance>
Date: Mon, 29 Sep 2025 15:51:58 +0800
From: Aaron Lu <ziqianlu@...edance.com>
To: Matteo Martelli <matteo.martelli@...ethink.co.uk>
Cc: Valentin Schneider <vschneid@...hat.com>,
	Ben Segall <bsegall@...gle.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	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>,
	Chuyi Zhou <zhouchuyi@...edance.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Florian Bezdeka <florian.bezdeka@...mens.com>,
	Songtang Liu <liusongtang@...edance.com>,
	Chen Yu <yu.c.chen@...el.com>,
	Michal Koutný <mkoutny@...e.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH 1/4] sched/fair: Propagate load for throttled cfs_rq

On Tue, Sep 23, 2025 at 03:05:29PM +0200, Matteo Martelli wrote:
> Hi Aaron,
> 
> On Wed, 10 Sep 2025 17:50:41 +0800, Aaron Lu <ziqianlu@...edance.com> wrote:
> > Before task based throttle model, propagating load will stop at a
> > throttled cfs_rq and that propagate will happen on unthrottle time by
> > update_load_avg().
> > 
> > Now that there is no update_load_avg() on unthrottle for throttled
> > cfs_rq and all load tracking is done by task related operations, let the
> > propagate happen immediately.
> > 
> > While at it, add a comment to explain why cfs_rqs that are not affected
> > by throttle have to be added to leaf cfs_rq list in
> > propagate_entity_cfs_rq() per my understanding of commit 0258bdfaff5b
> > ("sched/fair: Fix unfairness caused by missing load decay").
> > 
> > Signed-off-by: Aaron Lu <ziqianlu@...edance.com>
> > ---
> 
> I have been testing again the patch set "[PATCH v4 0/5] Defer throttle
> when task exits to user" [1] together with these follow up patches. I
> found out that with this patch the kernel sometimes produces the warning
> WARN_ON_ONCE(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list); in
> assert_list_leaf_cfs_rq() called by enqueue_task_fair(). I could
> reproduce this systematically by applying both [1] and this patch on top
> of tag v6.17-rc6 and also by directly testing at commit fe8d238e646e
> from sched/core branch of tip tree. I couldn't reproduce the warning by
> testing at commmit 5b726e9bf954 ("sched/fair: Get rid of
> throttled_lb_pair()").

Just a note that while trying to reproduce this problem, I noticed a
warn triggered in tg_throttle_down() with one setup. It's a different
problem and I've sent a patch to address that:
https://lore.kernel.org/lkml/20250929074645.416-1-ziqianlu@bytedance.com/