linux-kernel - Re: sched: Move SCHED

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Date:   Tue, 27 Apr 2021 17:17:09 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     peterz@...radead.org, bristot@...hat.com, bsegall@...gle.com,
        dietmar.eggemann@....com, greg@...ah.com,
        gregkh@...uxfoundation.org, joshdon@...gle.com,
        juri.lelli@...hat.com, linux-kernel@...r.kernel.org,
        linux@...musvillemoes.dk, mgorman@...e.de, mingo@...nel.org,
        valentin.schneider@....com, vincent.guittot@...aro.org,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: sched: Move SCHED_DEBUG sysctl to debugfs



On 27.04.21 17:09, Steven Rostedt wrote:
> On Tue, 27 Apr 2021 16:59:25 +0200
> Christian Borntraeger <borntraeger@...ibm.com> wrote:
> 
>> Peter,
>>
>> I just realized that we moved away sysctl tunabled to debugfs in next.
>> We have seen several cases where it was benefitial to set
>> sched_migration_cost_ns to a lower value. For example with KVM I can
>> easily get 50% more transactions with 50000 instead of 500000.
>> Until now it was possible to use tuned or /etc/sysctl.conf to set
>> these things permanently.
>>
>> Given that some people do not want to have debugfs mounted all the time
>> I would consider this a regression. The sysctl tunable was always
>> available.
>>
>> I am ok with the "informational" things being in debugfs, but not
>> the tunables. So how do we proceed here?
> 
> Should there be a schedfs created?
> 
> This is the reason I created the tracefs file system, was to get the
> tracing code out of debugfs, as debugfs is a catch all for everything and
> can lead to poor and insecure interfaces that people do not want to add on
> systems that they still want tracing on.
> 
> Or perhaps we should add a "tunefs" for tunables that are stable interfaces
> that should not be in /proc but also not in debugfs.

Yes, a tunefs or schedfs could be considered a replacement for sysctl.
It will still break existing setups with kernel.sched* things in /etc/sysctl.conf
but at least there is a stable transition path.