From: Peter Zijlstra <peterz@infradead.org>
To: Juri Lelli <juri.lelli@arm.com>
Cc: Byungchul Park <byungchul.park@lge.com>,
mingo@kernel.org, joel.opensrc@gmail.com,
linux-kernel@vger.kernel.org, juri.lelli@gmail.com,
rostedt@goodmis.org, kernel-team@lge.com
Subject: Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
Date: Mon, 21 Aug 2017 15:56:45 +0200 [thread overview]
Message-ID: <20170821135645.y3ppzdyewwbecvvx@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20170821134458.gocjoobaybb45egi@e106622-lin>
On Mon, Aug 21, 2017 at 02:44:58PM +0100, Juri Lelli wrote:
> Also, I'm not sure what Peter meant with
>
> "But still this isn't quite right, because when we consider this for SMT
> (as was the intent here) we'll happily occupy a full sibling core over
> finding an empty one."
Consider a 4 core, SMT2 system:
LLC [0 - 7]
SMT [0,1] [2,3] [4,5] [6,7]
If we do a wake-up on CPU0, we'll find CPU1, mark that as fallback,
continue up the domain tree, exclude 0,1 from 0-7 and find CPU2.
A next wakeup on CPU0 does the same and will find CPU3, fully loading
that core, instead of considering CPU4 first.
Doing this 'right' is difficult and expensive :-/
next prev parent reply other threads:[~2017-08-21 13:56 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-18 8:21 [PATCH v8 0/2] Make find_later_rq() choose a closer cpu in topology Byungchul Park
2017-08-18 8:21 ` [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park
2017-08-21 13:44 ` Juri Lelli
2017-08-21 13:56 ` Peter Zijlstra [this message]
2017-08-21 14:07 ` Juri Lelli
2017-08-22 5:55 ` Byungchul Park
2017-08-22 5:53 ` Byungchul Park
2017-08-22 7:12 ` Byungchul Park
2017-08-22 7:42 ` Juri Lelli
2017-08-18 8:21 ` [PATCH v8 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() Byungchul Park
2017-08-18 13:38 ` Steven Rostedt
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