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From: Rik van Riel <riel@surriel.com>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Valentin Schneider <valentin.schneider@arm.com>
Subject: Re: [PATCH v2] sched/fair: bring back select_idle_smt, but differently
Date: Mon, 22 Mar 2021 22:08:07 -0400	[thread overview]
Message-ID: <b81a0e641e6724c8aaf5b6a4b32fa4b550ecbbcd.camel@surriel.com> (raw)
In-Reply-To: <20210322153320.GG3697@techsingularity.net>

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On Mon, 2021-03-22 at 15:33 +0000, Mel Gorman wrote:

> If trying that, I would put that in a separate patch. At one point
> I did play with clearing prev, target and recent but hit problems.
> Initialising the mask and clearing them in select_idle_sibling() hurt
> the fast path and doing it later was not much better. IIRC, the
> problem
> I hit was that the cost of clearing multiple CPUs before the search
> was
> not offset by gains from a more efficient search.

I'm definitely avoiding the more expensive operations,
and am only using __cpumask_clear_cpu now :)

> If I had to guess, simply initialising cpumask after calling
> select_idle_smt() will be faster for your particular case because you
> have a reasonable expectation that prev's SMT sibling is idle when
> there
> are no idle cores. Checking if prev's sibling is free when there are
> no
> idle cores is fairly cheap in comparison to a cpumask initialisation
> and
> partial clearing.
> 
> If you have the testing capacity and time, test both.

Kicking off more tests soon. I'll get back with a v3 patch
on Wednesday.

-- 
All Rights Reversed.

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  reply	other threads:[~2021-03-23  2:09 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-21 19:03 [PATCH v2] sched/fair: bring back select_idle_smt, but differently Rik van Riel
2021-03-22 11:03 ` Mel Gorman
2021-03-22 15:07   ` Rik van Riel
2021-03-22 15:33     ` Mel Gorman
2021-03-23  2:08       ` Rik van Riel [this message]
2021-03-26 19:19   ` [PATCH v3] " Rik van Riel
2021-03-28 15:36     ` Mel Gorman
2021-04-06 15:10     ` Vincent Guittot
2021-04-06 15:26       ` Rik van Riel
2021-04-06 15:31         ` Vincent Guittot
2021-04-06 15:33           ` Vincent Guittot
2021-04-06 15:55           ` Rik van Riel
2021-04-06 16:13             ` Vincent Guittot
2021-04-07  7:17         ` Peter Zijlstra
2021-04-07  9:41           ` Mel Gorman
2021-04-07 10:15             ` Peter Zijlstra
2021-04-07 10:47               ` Mel Gorman
2021-04-07 12:10                 ` Peter Zijlstra
2021-04-07  9:42           ` Vincent Guittot
2021-04-07  9:54             ` Peter Zijlstra
2021-04-07  9:57               ` Vincent Guittot
2021-04-07 10:19               ` Peter Zijlstra
2021-04-07 10:24                 ` Vincent Guittot
2021-04-08 15:52                 ` Rik van Riel
2021-04-09 11:24     ` [tip: sched/core] sched/fair: Bring back select_idle_smt(), " tip-bot2 for Rik van Riel
2021-04-09 16:14     ` tip-bot2 for Rik van Riel

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