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From: Peter Zijlstra <peterz@infradead.org>
To: Mel Gorman <mgorman@suse.de>
Cc: "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 15:25:14 +0000	[thread overview]
Message-ID: <20201022152514.GJ2611@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201022145250.GK32041@suse.de>

On Thu, Oct 22, 2020 at 03:52:50PM +0100, Mel Gorman wrote:

> There are some questions
> currently on whether schedutil is good enough when HWP is not available.

Srinivas and Rafael will know better, but Intel does run a lot of tests
and IIRC it was found that schedutil was on-par for !HWP. That was the
basis for commit:

  33aa46f252c7 ("cpufreq: intel_pstate: Use passive mode by default without HWP")

But now it turns out that commit results in running intel_pstate-passive
on ondemand, which is quite horrible.

> 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 seems to be the question; Rafael just said the opposite.

> 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

s/HWP/cpufreq-governors/ ? But yes.

> 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.

Which is why I advocated to make it 'difficult' to use the old ones and
only later remove them.

> 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.

I remember :-)

  parent reply	other threads:[~2020-10-22 15:25 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
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 [this message]
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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