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Date: Mon, 2 Aug 2010 21:56:10 -0700
Message-ID: <AANLkTi=a-1hn_oL=i-=RKK9xOur+4mQjTRut+aiXtYkE@mail.gmail.com>
Subject: Re: Attempted summary of suspend-blockers LKML thread
From: =?ISO-8859-1?Q?Arve_Hj=F8nnev=E5g?= <arve@android.com>
To: paulmck@linux.vnet.ibm.com
Cc: Arjan van de Ven <arjan@infradead.org>,
        linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        mjg59@srcf.ucam.org, pavel@ucw.cz, florian@mickler.org, rjw@sisk.pl,
        stern@rowland.harvard.edu, swetland@google.com, peterz@infradead.org,
        tglx@linutronix.de, alan@lxorguk.ukuu.org.uk
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On Sun, Aug 1, 2010 at 6:10 PM, Paul E. McKenney
<paulmck@linux.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 Hj?nnev?g
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