linux-kernel - Re: [patch 2/2] sched/debug: Remove need

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Message-ID: <185e7b11-36aa-ffa8-7556-70a2840bd3b6@google.com>
Date: Thu, 9 Jan 2025 16:22:52 -0800 (PST)
From: David Rientjes <rientjes@...gle.com>
To: Josh Don <joshdon@...gle.com>
cc: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>, 
    Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
    Juri Lelli <juri.lelli@...hat.com>, 
    Vincent Guittot <vincent.guittot@...aro.org>, 
    Dietmar Eggemann <dietmar.eggemann@....com>, 
    Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, 
    Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, 
    linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] sched/debug: Remove need_resched ratelimiting for
 warnings

On Thu, 9 Jan 2025, Josh Don wrote:

> > Otherwise, please take a look, is this what you had in mind?
> 
> I'm realizing now that we'll end up getting multiple splats for a
> single very long stall (one per the warning threshold). We could fix
> that by using a magic number rather than 0 here (such as U64_MAX), and
> then teach resched_latency() to bail out on this value.
> 

Ack, ok.  I'll drop this patch because I see that there are existing users 
(at least one NVMe library) that cares about tuning both of these values 
with what appears to be some amount of thought:

/sys/kernel/debug/sched/latency_warn_once=0
/sys/kernel/debug/sched/latency_warn_ms=16

and the intent was not that they get excessive output that they don't need 
or aren't expecting.  Thanks for looking at this!