linux-kernel - Re: [PATCH] sched/fair: Fix inaccurate h_nr_runnable accounting with delayed dequeue

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Message-ID: <20250120050639.48966-1-vineethr@linux.ibm.com>
Date: Mon, 20 Jan 2025 10:36:39 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: kprateek.nayak@....com
Cc: bsegall@...gle.com, dietmar.eggemann@....com, gautham.shenoy@....com,
        juri.lelli@...hat.com, linux-kernel@...r.kernel.org, mgorman@...e.de,
        mingo@...hat.com, peterz@...radead.org, rostedt@...dmis.org,
        swapnil.sapkal@....com, vincent.guittot@...aro.org,
        vschneid@...hat.com, vineethr@...ux.ibm.com
Subject: Re: [PATCH] sched/fair: Fix inaccurate h_nr_runnable accounting with delayed dequeue

Hi Prateek,

>A SCHED_WARN_ON() to inspect h_nr_runnable post its update in
>dequeue_entities() like below:
>
>    cfs_rq->h_nr_runnable -= h_nr_runnable;
>    SCHED_WARN_ON(((int) cfs_rq->h_nr_runnable) < 0);
>
>is consistently tripped when running wakeup intensive workloads like
>hackbench in a cgroup.

I observed that the WARN_ON is triggered during the boot process without
the patch, and the patch resolves the issue.

However, I was unable to trigger the WARN_ON by running hackbench in a
cgroup without the patch. Could you please share the specific test
scenario or configuration you used to reproduce it?

For the boot process scenario:
Tested-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>

Thanks,
Madadi Vineeth Reddy