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From: Steven Rostedt <rostedt@goodmis.org>
To: Juri Lelli <juri.lelli@arm.com>
Cc: Byungchul Park <byungchul.park@lge.com>,
	peterz@infradead.org, mingo@kernel.org,
	linux-kernel@vger.kernel.org, juri.lelli@gmail.com,
	bristot@redhat.com, kernel-team@lge.com
Subject: Re: [PATCH v4 1/5] sched/deadline: Refer to cpudl.elements atomically
Date: Tue, 16 May 2017 09:10:53 -0400	[thread overview]
Message-ID: <20170516091053.5f0868b5@gandalf.local.home> (raw)
In-Reply-To: <20170516103241.xony5rtmqi66gczy@e106622-lin>

On Tue, 16 May 2017 11:32:41 +0100
Juri Lelli <juri.lelli@arm.com> wrote:


> Not sure, but if we are going to retry a lot it might be better off to
> put proper locking instead? We could also simply bail out when we notice

Actually, locking can make it much worse. I've been playing with RT on
boxes with 240 cores (with HT turned off!), and *any* locks in the
scheduler can cause huge contention.

> that something is changed under our feet. I'd say (again :) we might
> first want to understand (with some numbers) how bad the problem is and
> then fix it. I guess numbers might also help us to better understand
> what the best fix is?

Exactly. I haven't seen any numbers. Yes, it is not perfect, but we
don't know how unperfect it is. Numbers will help to know if there is
even a problem or not with the current solution.

-- Steve

  reply	other threads:[~2017-05-16 13:11 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-12  5:48 [PATCH v4 0/5] Make find_later_rq() choose a closer cpu in topology Byungchul Park
2017-05-12  5:48 ` [PATCH v4 1/5] sched/deadline: Refer to cpudl.elements atomically Byungchul Park
2017-05-12 14:25   ` Steven Rostedt
2017-05-15  8:36     ` Juri Lelli
2017-05-16  7:00       ` Byungchul Park
2017-05-16  6:52     ` Byungchul Park
2017-05-16 10:32       ` Juri Lelli
2017-05-16 13:10         ` Steven Rostedt [this message]
2017-05-23  1:11           ` Byungchul Park
2017-05-12  5:48 ` [PATCH v4 2/5] sched/deadline: Make find_later_rq() choose a closer cpu in topology Byungchul Park
2017-05-12  5:48 ` [PATCH v4 3/5] sched/deadline: Change return value of cpudl_find() Byungchul Park
2017-05-12  5:48 ` [PATCH v4 4/5] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park
2017-05-12  5:48 ` [PATCH v4 5/5] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() Byungchul Park

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