From: Peter Zijlstra <peterz@infradead.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Rik van Riel <riel@surriel.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Kernel Team <kernel-team@fb.com>, Ingo Molnar <mingo@kernel.org>,
Valentin Schneider <valentin.schneider@arm.com>
Subject: Re: [PATCH v3] sched/fair: bring back select_idle_smt, but differently
Date: Wed, 7 Apr 2021 14:10:44 +0200 [thread overview]
Message-ID: <YG2hRBnf16raGy63@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210407104717.GD3697@techsingularity.net>
On Wed, Apr 07, 2021 at 11:47:17AM +0100, Mel Gorman wrote:
> Ok, cpusets do split domains. I can't imagine the logic of splitting SMT
> siblings across cpusets but if it's possible, it has to be checked and
> protecting that with cpusets_enabled() would be a little overkill and
> possibly miss some other corner case :(
Quite. The logic is that some people can't be arsed to look at how the
topology is enumerated and simply split logical CPUs by a random number.
Imagine we have 4 cores, with 2 threads each, for 8 logical CPUs.
Suppose you want a partition of 6 'cpus' and 2 spares. Hoping for a 3:1
core split.
If things are enumerated like: core0{smt0, smt1}, core1{smt0, smt1} ...
then 0-5 will get you 3 whole cores.
If OTOH things are enumerated like: smt0{core0, core1, core2, core3},
smt1{...} then 0-5 will get you the loonie side of the moon.
Funny thing is that x86 can iterate either way depending on how the BIOS
monkey filled out the tables.
next prev parent reply other threads:[~2021-04-07 12:11 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-21 19:03 [PATCH v2] " 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
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 [this message]
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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