Re: sched: Move SCHED_DEBUG sysctl to debugfs

[Christian Borntraeger]

On 27.04.21 17:09, Steven Rostedt wrote:
> On Tue, 27 Apr 2021 16:59:25 +0200
> Christian Borntraeger <borntraeger@xxxxxxxxxx> 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.