[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZR05JXPgOXb4kuHl@gmail.com>
Date: Wed, 4 Oct 2023 12:06:29 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
linux-kernel@...r.kernel.org, Phil Auld <pauld@...hat.com>,
Brent Rowsell <browsell@...hat.com>,
Peter Hunt <pehunt@...hat.com>,
Florian Weimer <fweimer@...hat.com>
Subject: Re: [PATCH v4] sched/core: Use zero length to reset cpumasks in
sched_setaffinity()
* Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Oct 04, 2023 at 11:23:41AM +0200, Ingo Molnar wrote:
>
> > > if (user_mask) {
> > > - cpumask_copy(user_mask, in_mask);
> > > + /*
> > > + * All-set user cpumask resets affinity and drops the explicit
> > > + * user mask.
> > > + */
> > > + cpumask_and(user_mask, in_mask, cpu_possible_mask);
> > > + if (cpumask_equal(user_mask, cpu_possible_mask)) {
> > > + kfree(user_mask);
> > > + user_mask = NULL;
> > > + }
> >
> > Question: is there any observable behavioral difference between current
> > (old) all-set cpumask calls and the patched (new) one?
>
> Very little I think -- the main difference is that we no longer carry
> the ->user_cpus_ptr mask around, and that saves a little masking.
So calling with a full mask would actually work fine on 'old' kernels too,
as it's a 'reset' event in essence. (With a bit of allocation & masking
overhead.)
This pretty unambiguously marks the full-mask solution as the superior ABI ...
Thanks,
Ingo
Powered by blists - more mailing lists