From: Phil Auld <pauld@redhat.com>
To: Colin Ian King <colin.king@canonical.com>
Cc: Mel Gorman <mgorman@suse.de>,
Peter Zijlstra <peterz@infradead.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Giovanni Gherdovich <ggherdovich@suse.com>,
Viresh Kumar <viresh.kumar@linaro.org>,
Julia Lawall <julia.lawall@inria.fr>,
Ingo Molnar <mingo@redhat.com>,
kernel-janitors@vger.kernel.org,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
linux-kernel@vger.kernel.org,
Valentin Schneider <valentin.schneider@arm.com>,
Gilles Muller <Gilles.Muller@inria.fr>,
srinivas.pandruvada@linux.intel.com,
Linux PM <linux-pm@vger.kernel.org>,
Len Brown <len.brown@intel.com>
Subject: Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core
Date: Thu, 22 Oct 2020 15:12:00 +0000 [thread overview]
Message-ID: <20201022151200.GC92942@lorien.usersys.redhat.com> (raw)
In-Reply-To: <6606e5f4-3f66-5844-da02-5b11e1464be6@canonical.com>
On Thu, Oct 22, 2020 at 03:58:13PM +0100 Colin Ian King wrote:
> On 22/10/2020 15:52, Mel Gorman wrote:
> > On Thu, Oct 22, 2020 at 02:29:49PM +0200, Peter Zijlstra wrote:
> >> On Thu, Oct 22, 2020 at 02:19:29PM +0200, Rafael J. Wysocki wrote:
> >>>> However I do want to retire ondemand, conservative and also very much
> >>>> intel_pstate/active mode.
> >>>
> >>> I agree in general, but IMO it would not be prudent to do that without making
> >>> schedutil provide the same level of performance in all of the relevant use
> >>> cases.
> >>
> >> Agreed; I though to have understood we were there already.
> >
> > AFAIK, not quite (added Giovanni as he has been paying more attention).
> > Schedutil has improved since it was merged but not to the extent where
> > it is a drop-in replacement. The standard it needs to meet is that
> > it is at least equivalent to powersave (in intel_pstate language)
> > or ondemand (acpi_cpufreq) and within a reasonable percentage of the
> > performance governor. Defaulting to performance is a) giving up and b)
> > the performance governor is not a universal win. There are some questions
> > currently on whether schedutil is good enough when HWP is not available.
> > There was some evidence (I don't have the data, Giovanni was looking into
> > it) that HWP was a requirement to make schedutil work well. That is a
> > hazard in itself because someone could test on the latest gen Intel CPU
> > and conclude everything is fine and miss that Intel-specific technology
> > is needed to make it work well while throwing everyone else under a bus.
> > Giovanni knows a lot more than I do about this, I could be wrong or
> > forgetting things.
> >
> > For distros, switching to schedutil by default would be nice because
> > frequency selection state would follow the task instead of being per-cpu
> > and we could stop worrying about different HWP implementations but it's
> > not at the point where the switch is advisable. I would expect hard data
> > before switching the default and still would strongly advise having a
> > period of time where we can fall back when someone inevitably finds a
> > new corner case or exception.
>
> ..and it would be really useful for distros to know when the hard data
> is available so that they can make an informed decision when to move to
> schedutil.
>
I think distros are on the hook to generate that hard data themselves
with which to make such a decision. I don't expect it to be done by
someone else.
> >
> > For reference, SLUB had the same problem for years. It was switched
> > on by default in the kernel config but it was a long time before
> > SLUB was generally equivalent to SLAB in terms of performance. Block
> > multiqueue also had vaguely similar issues before the default changes
> > and a period of time before it was removed removed (example whinging mail
> > https://lore.kernel.org/lkml/20170803085115.r2jfz2lofy5spfdb@techsingularity.net/)
> > It's schedutil's turn :P
> >
>
Agreed. I'd like the option to switch back if we make the default change.
It's on the table and I'd like to be able to go that way.
Cheers,
Phil
--
next prev parent reply other threads:[~2020-10-22 15:12 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-20 16:37 [PATCH] sched/fair: check for idle core Julia Lawall
2020-10-21 7:29 ` Vincent Guittot
2020-10-21 11:13 ` Peter Zijlstra
2020-10-21 12:27 ` Vincent Guittot
2020-10-21 11:20 ` Mel Gorman
2020-10-21 11:56 ` Julia Lawall
2020-10-21 12:19 ` Peter Zijlstra
2020-10-21 12:42 ` Julia Lawall
2020-10-21 12:52 ` Peter Zijlstra
2020-10-21 18:18 ` Rafael J. Wysocki
2020-10-21 18:15 ` Rafael J. Wysocki
2020-10-21 19:47 ` Julia Lawall
2020-10-21 20:25 ` Rafael J. Wysocki
2020-10-21 13:10 ` Peter Zijlstra
2020-10-21 18:11 ` Rafael J. Wysocki
2020-10-22 4:53 ` Viresh Kumar
2020-10-22 7:11 ` Peter Zijlstra
2020-10-22 10:59 ` Viresh Kumar
2020-10-22 11:45 ` Rafael J. Wysocki
2020-10-22 12:02 ` default cpufreq gov, was: " Peter Zijlstra
2020-10-22 12:19 ` Rafael J. Wysocki
2020-10-22 12:29 ` Peter Zijlstra
2020-10-22 14:52 ` Mel Gorman
2020-10-22 14:58 ` Colin Ian King
2020-10-22 15:12 ` Phil Auld [this message]
2020-10-22 16:35 ` Mel Gorman
2020-10-22 17:59 ` Rafael J. Wysocki
2020-10-22 20:32 ` Mel Gorman
2020-10-22 20:39 ` Phil Auld
2020-10-22 15:25 ` Peter Zijlstra
2020-10-22 15:55 ` Rafael J. Wysocki
2020-10-22 16:29 ` Mel Gorman
2020-10-22 20:10 ` Giovanni Gherdovich
2020-10-22 20:16 ` Giovanni Gherdovich
2020-10-23 7:03 ` Peter Zijlstra
2020-10-23 17:46 ` Tom Lendacky
2020-10-26 19:52 ` Fontenot, Nathan
2020-10-22 15:45 ` A L
2020-10-22 15:55 ` Vincent Guittot
2020-10-23 5:23 ` Viresh Kumar
2020-10-22 16:23 ` [PATCH] cpufreq: Avoid configuring old governors as default with intel_pstate Rafael J. Wysocki
2020-10-23 6:29 ` Viresh Kumar
2020-10-23 11:59 ` Rafael J. Wysocki
2020-10-23 15:15 ` [PATCH v2] " Rafael J. Wysocki
2020-10-27 3:13 ` Viresh Kumar
2020-10-27 11:11 ` default cpufreq gov, was: [PATCH] sched/fair: check for idle core Qais Yousef
2020-10-27 11:26 ` Valentin Schneider
2020-10-27 11:42 ` Qais Yousef
2020-10-27 11:48 ` Viresh Kumar
2020-10-23 6:24 ` Viresh Kumar
2020-10-23 15:06 ` Rafael J. Wysocki
2020-10-27 3:13 ` Viresh Kumar
2020-10-22 11:21 ` AW: " Walter Harms
2020-10-21 12:28 ` Mel Gorman
2020-10-21 12:25 ` Vincent Guittot
2020-10-21 12:47 ` Mel Gorman
2020-10-21 12:56 ` Julia Lawall
2020-10-21 13:18 ` Mel Gorman
2020-10-21 13:24 ` Julia Lawall
2020-10-21 15:08 ` Mel Gorman
2020-10-21 15:18 ` Julia Lawall
2020-10-21 15:23 ` Vincent Guittot
2020-10-21 15:33 ` Julia Lawall
2020-10-21 15:19 ` Vincent Guittot
2020-10-21 17:00 ` Mel Gorman
2020-10-21 17:39 ` Julia Lawall
2020-10-21 13:48 ` Julia Lawall
2020-10-21 15:26 ` Mel Gorman
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