linux-kernel - Re: [PATCH 6/6] Makes procs file writable to move all threads by tgid at once

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Message-ID: <20090804190139.GA9896@us.ibm.com>
Date:	Tue, 4 Aug 2009 14:01:39 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Paul Menage <menage@...gle.com>
Cc:	Benjamin Blum <bblum@...gle.com>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 6/6] Makes procs file writable to move all threads by
	tgid at once

Quoting Paul Menage (menage@...gle.com):
> On Mon, Aug 3, 2009 at 12:45 PM, Serge E. Hallyn<serue@...ibm.com> wrote:
> >
> > This is probably a stupid idea, but...  what about having zero
> > overhead at clone(), and instead, at cgroup_task_migrate(),
> > dequeue_task()ing all of the affected threads for the duration of
> > the migrate?
> >
> 
> Or a simpler alternative - rather than taking the thread group
> leader's rwsem in cgroup_fork(), always take current's rwsem. Then
> you're always locking a (probably?) local rwsem and minimizing the
> overhead. So not quite zero overhead in the fork path, but I'd be
> surprised if it was measurable. In cgroup_attach_proc() you then have
> to take the rwsem of every thread in the process. Kind of the
> equivalent of a per-threadgroup big-reader lock.
> 
> Paul

Yup I think that would addres my concern (cache-line bouncing in hot
clone(CLONE_THREAD) case).

thanks,
-serge
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