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Message-ID: <598033f7-f937-4d32-a4ec-b3e0d094c637@antgroup.com>
Date:   Sat, 09 Dec 2023 12:51:27 +0800
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Subject: Re: [PATCH -tip] sched/fair: gracefully handle EEVDF scheduling
 failures
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To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mingo@kernel.org, wuyun.abel@bytedance.com,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        linux-kernel@vger.kernel.org
References: <20231208112100.18141-1-tiwei.btw@antgroup.com>
 <20231208143208.GF28727@noisy.programming.kicks-ass.net>
From:   "Tiwei Bie" <tiwei.btw@antgroup.com>
In-Reply-To: <20231208143208.GF28727@noisy.programming.kicks-ass.net>
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On 12/8/23 10:32 PM, Peter Zijlstra wrote:
> On Fri, Dec 08, 2023 at 07:20:59PM +0800, Tiwei Bie wrote:
>> The EEVDF scheduling might fail due to unforeseen issues. Previously,
> 
> I might also fly if I jump up. But is there any actual reason to believe
> something like that will happen?

Thanks for the quick reply! Sorry, after re-reading the commit log,
it looks confusing to me as well. I didn't mean something like that
will happen. I just thought it might be worthwhile to have a sanity
check on 'best'. Because, the 'best' is initialized to NULL and is
conditionally updated. The added 'WARN_ONCE' on '!best' is more like
a 'default' case to catch an unreachable case in a 'switch' block.
There was a similar check in the past that was helpful. And there
seems to be no harm in doing it. If this is reasonable, I'd like to
submit a v2 patch.

PS. I just noticed that the subject line should start with a uppercase
letter according to the rules in the tip tree handbook [1]. The subject
line should be something like: "sched/fair: Sanity check best in pick_eevdf()".

[1] https://www.kernel.org/doc/html/next/process/maintainer-tip.html#patch-subject

Regards,
Tiwei