linux-kernel - Re: [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting

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Message-ID: <dfd21361-1776-16db-c37b-cecc5ebe6db5@arm.com>
Date:   Thu, 16 Aug 2018 15:45:45 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Quentin Perret <quentin.perret@....com>,
        Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups
 accounting

On 08/16/2018 03:37 PM, Quentin Perret wrote:
>>> IMHO, if this is something which should not happen at all, a BUG_ON() is the
>>> right thing to do here.
>>
>> I don't agree on that. I agree it should not happen but since it's a
>> recoverable error it think we should not panic.
> 
> FWIW, if this is a recoverable error, I think Linus will agree with
> Patrick on this one :-)
> 
> https://lkml.org/lkml/2016/10/4/1

Yeah, not really agreeing here that this is a recoverable error. 
Besides, we only consider under-run here, what about over-run?

Currently this warning doesn't hit and if the code will be changed and 
it hits, I still find a BUG_ON more appealing here ...

So this error scenario can happen over and over again and we always 
recover from ? The important thing is that we find the culprit for this 
behaviour as fast as possible ...

Warning or bug, at least a stack trace is necessary.