linux-kernel - Re: A Plumber’s Wish List for Linux

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Message-ID: <CALdu-PAMNK5dBAf9kB8_uQf8uQhrzSfRm+4sOqTG40KjsG5U+A@mail.gmail.com>
Date:	Wed, 19 Oct 2011 14:19:37 -0700
From:	Paul Menage <paul@...lmenage.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org, lennart@...ttering.net,
	harald@...hat.com, david@...ar.dk, greg@...ah.com,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Oleg Nesterov <oleg@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: A Plumber’s Wish List for Linux

On Fri, Oct 14, 2011 at 8:38 AM, Frederic Weisbecker <fweisbec@...il.com> wrote:
>
> Well, wouldn't it be better to pull that complexity to userspace?
> After all, moving tasks from a cgroup to another is not a performance
> critical operation so that probably doesn't need to be all handled by
> the kernel.

I'd always assumed that too, but apparently on very many (possibly the
majority of?) Linux systems, it actually is performance-critical.

Specifically, Android bounces tasks in and out of a "foreground
low-latency" cpu cgroup at a fairly high rate, and has found the
performance hit from the locking to be a problem on multi-core phones.
Hence Colin Cross' patches for avoid calls to synchronize_rcu() in the
attach path.

Paul
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