linux-kernel - Re: [PATCH v2 7/9] sched,debug: Convert sysctl sched

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Message-ID: <a3399de6-ebe9-a813-23a1-565f6fdf38c7@arm.com>
Date:   Thu, 15 Apr 2021 14:16:14 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>
Cc:     mingo@...nel.org, mgorman@...e.de, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        bsegall@...gle.com, bristot@...hat.com, joshdon@...gle.com,
        linux-kernel@...r.kernel.org, greg@...ah.com,
        linux@...musvillemoes.dk
Subject: Re: [PATCH v2 7/9] sched,debug: Convert sysctl sched_domains to
 debugfs

On 15/04/2021 11:06, Peter Zijlstra wrote:
> On Tue, Apr 13, 2021 at 03:55:15PM +0100, Valentin Schneider wrote:
>> On 12/04/21 12:14, Peter Zijlstra wrote:
>>> Stop polluting sysctl, move to debugfs for SCHED_DEBUG stuff.
>>>
>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>>> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
>>
>> On my Juno (2+4 big.LITTLE), sys/kernel/debug/sched/domains/ is now empty.
>>
>> I think that's because of unregister_sched_domain_sysctl() -
>> debugfs_remove() is recursive, and I do get a case where we rebuild the
>> domains but no CPU has been added or removed (we rebuild the domains when
>> cpufreq kicks in, it's part of the big.LITTLE ponies).
>>
>> Do we actually still need that unregister? From a brief glance it looks
>> like we could throw it out.
> 
> Yeah, I can't think of anything either. AFAICT it hasn't done anything
> useful since that cpumask optimization. Consider it gone.
> 
> I'll let it soak for another day or so, but then I was planning on
> merging this series.
> 
> Updated patch has been in queue.git/sched/debug since yesterday.

Had to check since v1 was working fine on Juno. So it was this
__cpumask_clear_cpu() in register_sched_domain_sysctl() introduced in v2
which let the files under /sys/kernel/debug/sched/domains disapear.

With {un,}register_sched_domain_sysctl() removed from
partition_sched_domains_locked() they're there again.

Looks like now register_sched_domain_sysctl() can be made static in
kernel/sched/debug.c.

[...]