linux-kernel - Re: [PATCH RFC] workqueue: Make show

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Date:   Fri, 6 Jan 2023 14:24:29 -1000
From:   Tejun Heo <tj@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        Dave Jones <davej@...emonkey.org.uk>,
        Rik van Riel <riel@...riel.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] workqueue: Make show_pwq() use run-length encoding

On Fri, Jan 06, 2023 at 04:10:24PM -0800, Paul E. McKenney wrote:
> The show_pwq() function dumps out a pool_workqueue structure's activity,
> including the pending work-queue handlers:
> 
>  Showing busy workqueues and worker pools:
>  workqueue events: flags=0x0
>    pwq 0: cpus=0 node=0 flags=0x1 nice=0 active=10/256 refcnt=11
>      in-flight: 7:test_work_func, 64:test_work_func, 249:test_work_func
>      pending: test_work_func, test_work_func, test_work_func1, test_work_func1, test_work_func1, test_work_func1, test_work_func1
> 
> When large systems are facing certain types of hang conditions, it is not
> unusual for this "pending" list to contain runs of hundreds of identical
> function names.  This "wall of text" is difficult to read, and worse yet,
> it can be interleaved with other output such as stack traces.
> 
> Therefore, make show_pwq() use run-length encoding so that the above
> printout instead looks like this:
> 
>  Showing busy workqueues and worker pools:
>  workqueue events: flags=0x0
>    pwq 0: cpus=0 node=0 flags=0x1 nice=0 active=10/256 refcnt=11
>      in-flight: 7:test_work_func, 64:test_work_func, 249:test_work_func
>      pending: 2*test_work_func, 5*test_work_func1
> 
> When no comma would be printed, including the WORK_STRUCT_LINKED case,
> a new run is started unconditionally.
> 
> This output is more readable, places less stress on the hardware,
> firmware, and software on the console-log path, and reduces interference
> with other output.

This is fantastic. Applied to wq/for-6.3.

Thanks.

-- 
tejun