linux-kernel - Re: [PATCH 2/3] sched, cgroup: replace signal_struct->group_rwsem with a global percpu

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Message-ID: <20150521203943.GS24861@htj.duckdns.org>
Date:	Thu, 21 May 2015 16:39:43 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Zefan Li <lizefan@...wei.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, cgroups@...r.kernel.org,
	mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] sched, cgroup: replace signal_struct->group_rwsem
 with a global percpu_rwsem

Hello, Li.

On Wed, May 20, 2015 at 06:05:37PM +0800, Zefan Li wrote:
> > The latency is bound by synchronize_sched_expedited().  Given the way
> > cgroups are used in majority of setups (process migration happening
> > only during service / session setups), I think this should be okay.
> 
> Actually process migration can happen quite frequently, for example in
> Android phones, and that's why Google had an out-of-tree patch to remove
> the synchronize_rcu() in that path, which turned out to be buggy.

It's still not a very frequent operation tho.  We're talking about
users switching fore/background jobs here and the expedited
synchronization w/ preemption enabled doesn't take much time.  In
addition, as it currently stands, android is doing memory charge
immigration on each fore/background switches.  I'm pretty doubtful
this would make any difference.

Thanks.

-- 
tejun
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