linux-kernel - Re: [PATCH 3/3] pids: Make it possible to clone tasks with given pids

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Date:	Fri, 11 Nov 2011 08:22:00 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Glauber Costa <glommer@...allels.com>,
	Nathan Lynch <ntl@...ox.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Serge Hallyn <serue@...ibm.com>,
	Daniel Lezcano <dlezcano@...ibm.com>
Subject: Re: [PATCH 3/3] pids: Make it possible to clone tasks with given
 pids

On Fri, Nov 11, 2011 at 08:18:19PM +0400, Pavel Emelyanov wrote:
> > To add a bit, it's also one of the more *serialized* path. Doing it in
> > parallel might actually hurt, 
> 
> Can you elaborate on this, please?

It goes through a lot of locks - tasklist_lock, mmlist_lock, other
subsys locks depending on CLONE_* options.  If you try to do that on
multiple CPUs in parallel, depending on the level of concurrency,
contention and extra cacheline bounces may dominate the overhead.

Thanks.

-- 
tejun
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