linux-kernel - Re: [patch 1/4] add basic task isolation prctl interface

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Date:   Wed, 28 Jul 2021 13:21:21 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     Nitesh Lal <nilal@...hat.com>
Cc:     Nicolas Saenz Julienne <nsaenzju@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alex Belits <abelits@...vell.com>,
        Peter Xu <peterx@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 1/4] add basic task isolation prctl interface

On Wed, Jul 28, 2021 at 11:00:01AM -0400, Nitesh Lal wrote:
> > > A latency sensitive
> > > application might be OK with the former but not with the latter.
> >
> > Two alternatives:
> >
> > 1) The pattern above, where particular subsystems that might interrupt
> > the kernel are enabled automatically if the kernel supports it.
> >
> > Pros:
> > Applications which implement this only need to be changed once,
> > and can benefit from new kernel features.
> >
> > Applications can disable particular features if they turn
> > out to be problematic.
> >
> > Cons:
> > New features might break applications.
> >
> > 2) Force applications to enable each new feature individually.
> >
> > Pros: Won't cause regressions, kernel behaviour is explicitly
> > controlled by userspace.
> >
> > Cons: Apps won't benefit from new features automatically.
> >
> > ---
> >
> > It seems to me 1) is preferred. Can also add a sysfs control to
> > have a "default_isolation_feature" flag, which can be changed
> > by a sysadmin in case a new feature is undesired.
> >
> > Thoughts?
> >
> >
> The first option may work specifically with the sysfs interface that you
> mentioned, however, IMHO (2) is safer than regressing the workloads. Also,
> if the previously implemented controls are good enough for the workload
> then there should not be a need to enable the new ones.

OK, can set default_isolation_feature as 0 then, which admin can 
configure to a non-default value. This would enable the new
features only if the admin enables them.

Thanks.