linux-kernel - Re: [PATCH 6/7] workqueue: Report work funcs that trigger automatic CPU

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Message-ID: <20230511212606.GI2296992@hirez.programming.kicks-ass.net>
Date:   Thu, 11 May 2023 23:26:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     jiangshanlai@...il.com, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH 6/7] workqueue: Report work funcs that trigger automatic
 CPU_INTENSIVE mechanism

On Thu, May 11, 2023 at 08:19:30AM -1000, Tejun Heo wrote:
> Workqueue now automatically marks per-cpu work items that hog CPU for too
> long as CPU_INTENSIVE, which excludes them from concurrency management and
> prevents stalling other concurrency-managed work items. If a work function
> keeps running over the thershold, it likely needs to be switched to use an
> unbound workqueue.
> 
> This patch adds a debug mechanism which tracks the work functions which
> trigger the automatic CPU_INTENSIVE mechanism and report them using
> pr_warn() with exponential backoff.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>

I did do wonder why you chose for external storage for this -- I figured
it was to keep the cost down since it shouldn't really be happening, so
storage in the normal data structures is a waste etc..?

Otherwise seems fine; thanks!