linux-kernel - Re: Attempted summary of suspend-blockers LKML thread

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Date:	Mon, 2 Aug 2010 21:56:10 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Arjan van de Ven <arjan@...radead.org>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	mjg59@...f.ucam.org, pavel@....cz, florian@...kler.org,
	rjw@...k.pl, stern@...land.harvard.edu, swetland@...gle.com,
	peterz@...radead.org, tglx@...utronix.de, alan@...rguk.ukuu.org.uk
Subject: Re: Attempted summary of suspend-blockers LKML thread

On Sun, Aug 1, 2010 at 6:10 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Sun, Aug 01, 2010 at 03:47:08PM -0700, Arjan van de Ven wrote:
...
>> Another one: freezing whole cgroups..... we have that today. it
>> actually works quite well.... of course the hard part is the decision
>> what to put in which cgroup, and at what frequency and duration you let
>> cgroups run.
>
> Indeed, the Android guys seemed to be quite excited by cgroup freezing
> until they thought about the application-classification problem.
> Seems like it should be easy for some types of applications, but I do
> admit that apps can have non-trivial and non-obvious dependencies.
>

The dependencies is what made this solution uninteresting to us. For
instance, we currently use cgroup scheduling to reduce the impact of
some background tasks, but we occasionally saw a watchdog restart of
the system process were critical services were waiting on a kernel
mutex owned by a background task for more than 20 seconds. If we froze
a cgroup instead, we would not hit this particular problem since tasks
cannot be frozen while executing kernel code the same way they can be
preempted, but nothing prevents a task from being frozen while holding
a user-space resource.

-- 
Arve Hjønnevåg
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