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From: Peter Zijlstra <peterz@infradead.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Galbraith <efault@gmx.de>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	LKML <linux-kernel@vger.kernel.org>,
	rjw@rjwysocki.net, srinivas.pandruvada@linux.intel.com
Subject: Re: [PATCH 4/4] sched/fair: Use a recently used CPU as an idle candidate and the basis for SIS
Date: Tue, 30 Jan 2018 14:40:49 +0100	[thread overview]
Message-ID: <20180130134049.GU2249@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180130132527.tjc6vea76sm5zm76@techsingularity.net>

On Tue, Jan 30, 2018 at 01:25:27PM +0000, Mel Gorman wrote:
> > Because, esp. in this scenario; a task migrating; the hardware really
> > can't do anything sensible, whereas the OS _knows_.
> 
> Potentially yes. One option without HWP would be to track utilisation
> for a task or artifically boost it for a short period after migration so
> a higher p-state is potentially selected. With HWP, a hint would have to
> be given to the hardware to try select a higher frequency but I've no idea
> how expensive that is or how it would behave on different implementations
> of HWP. It may also be a game of whack-a-mole trying to get every cpufreq
> configuration correct.

We have much of this infrastructure and have been working on improving
it [1]. We already track per task utilization and feed it into a cpufreq
governor (schedutil).

> One advantage of using fewer cores is that it should
> work regardless of cpufreq driver.

Sure, and I started out by saying this patch isn't necessarily bad; but
I think our 'use' [2] of HWP _is_.


[1] https://lkml.kernel.org/r/20180123180847.4477-1-patrick.bellasi@arm.com
[2] IIRC we basically don't do _anything_ when HWP.

  reply	other threads:[~2018-01-30 13:40 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-30 10:45 [PATCH 0/4] Reduce migrations and unnecessary spreading of load to multiple CPUs Mel Gorman
2018-01-30 10:45 ` [PATCH 1/4] sched/fair: Remove unnecessary parameters from wake_affine_idle Mel Gorman
2018-02-06 11:55   ` [tip:sched/urgent] sched/fair: Remove unnecessary parameters from wake_affine_idle() tip-bot for Mel Gorman
2018-01-30 10:45 ` [PATCH 2/4] sched/fair: Restructure wake_affine to return a CPU id Mel Gorman
2018-02-06 11:56   ` [tip:sched/urgent] sched/fair: Restructure wake_affine*() " tip-bot for Mel Gorman
2018-01-30 10:45 ` [PATCH 3/4] sched/fair: Do not migrate if the prev_cpu is idle Mel Gorman
2018-02-06 11:56   ` [tip:sched/urgent] " tip-bot for Mel Gorman
2018-01-30 10:45 ` [PATCH 4/4] sched/fair: Use a recently used CPU as an idle candidate and the basis for SIS Mel Gorman
2018-01-30 11:50   ` Peter Zijlstra
2018-01-30 12:57     ` Mel Gorman
2018-01-30 13:15       ` Peter Zijlstra
2018-01-30 13:25         ` Mel Gorman
2018-01-30 13:40           ` Peter Zijlstra [this message]
2018-01-30 14:06             ` Mel Gorman
2018-01-31  9:22         ` Rafael J. Wysocki
2018-01-31 10:17           ` Peter Zijlstra
2018-01-31 11:54             ` Mel Gorman
2018-01-31 17:44             ` Srinivas Pandruvada
2018-02-01  9:11               ` Peter Zijlstra
2018-02-01  7:50             ` Rafael J. Wysocki
2018-02-01  9:11               ` Peter Zijlstra
2018-02-01 13:18                 ` Srinivas Pandruvada
2018-02-02 11:00                   ` Rafael J. Wysocki
2018-02-02 14:54                     ` Srinivas Pandruvada
2018-02-02 19:48                       ` Mel Gorman
2018-02-02 20:01                         ` Srinivas Pandruvada
2018-02-05 11:10                           ` Mel Gorman
2018-02-05 17:04                             ` Srinivas Pandruvada
2018-02-05 17:50                               ` Mel Gorman
2018-02-04  8:42                         ` Rafael J. Wysocki
2018-02-04  8:38                       ` Rafael J. Wysocki
2018-02-02 11:42                 ` Rafael J. Wysocki
2018-02-02 12:46                   ` Peter Zijlstra
2018-02-02 12:55                     ` Peter Zijlstra
2018-02-02 14:08                     ` Peter Zijlstra
2018-02-03 16:30                       ` Srinivas Pandruvada
2018-02-05 10:44                         ` Peter Zijlstra
2018-02-05 10:58                           ` Ingo Molnar
2018-02-02 12:58                   ` Peter Zijlstra
2018-02-02 13:27                   ` Mel Gorman
2018-01-30 13:15       ` Mike Galbraith
2018-01-30 13:25         ` Peter Zijlstra
2018-01-30 13:35           ` Mike Galbraith
2018-01-30 11:53   ` Peter Zijlstra
2018-01-30 12:59     ` Mel Gorman
2018-01-30 13:06     ` Peter Zijlstra
2018-01-30 13:18       ` Mel Gorman
2018-02-06 11:56   ` [tip:sched/urgent] " tip-bot for Mel Gorman

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