linux-kernel - Re: [PATCH 02/10] freezer: skip waking up tasks with PF_FREEZER

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Message-ID: <20130429220831.GC2395@htj.dyndns.org>
Date:	Mon, 29 Apr 2013 15:08:31 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Colin Cross <ccross@...roid.com>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Arve Hjønnevåg <arve@...roid.com>,
	Li Zefan <lizefan@...wei.com>, Len Brown <len.brown@...el.com>,
	Pavel Machek <pavel@....cz>,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org
Subject: Re: [PATCH 02/10] freezer: skip waking up tasks with PF_FREEZER_SKIP
 set

Hey,

On Mon, Apr 29, 2013 at 03:02:19PM -0700, Colin Cross wrote:
> See the first patch in the series (which isn't available in the
> archive yet, so I can't link to it).  The short version is that

It didn't arrive in my lkml folder either.  Maybe vger is taking some
time distributing emails.

> Android goes through suspend/resume very often (every few seconds when
> on a busy wifi network with the screen off), and a significant portion
> of the energy used to go in and out of suspend is spent in the
> freezer.  This patch series takes the most common userspace sleep
> points and converts them to PF_FREEZER_SKIP, which reduces the number
> of context switches for every suspend or resume event on a
> freshly-booted Android device from 1000 to 25, and reduces the time

Ah, okay, so you're spreading PF_FREEZER_SKIP.  When you post patches
which touch the freezer can you please cc me and Oleg Nesterov
<oleg@...hat.com> (I'll ping him this time)?  Freezer has been very
subtly broken in various ways and many kthread users are still broken,
so let's tread carefully.

> spent freezing by a factor of 5.  It will have a similar effect on a
> non-Android system, although those generally don't care about
> suspend/resume optimization.

Yeah, if it's something which makes actual difference rather than
"this seems to be a good idea" thing, sure, let's find a way.

Thanks.

-- 
tejun
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