From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758051Ab1KKQWI (ORCPT ); Fri, 11 Nov 2011 11:22:08 -0500 Received: from mail-pz0-f42.google.com ([209.85.210.42]:63537 "EHLO mail-pz0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752116Ab1KKQWG (ORCPT ); Fri, 11 Nov 2011 11:22:06 -0500 Date: Fri, 11 Nov 2011 08:22:00 -0800 From: Tejun Heo To: Pavel Emelyanov Cc: Oleg Nesterov , Andrew Morton , Cyrill Gorcunov , Glauber Costa , Nathan Lynch , Linux Kernel Mailing List , Serge Hallyn , Daniel Lezcano Subject: Re: [PATCH 3/3] pids: Make it possible to clone tasks with given pids Message-ID: <20111111162200.GA24737@google.com> References: <4EBC0696.9030103@parallels.com> <4EBC06DB.3090202@parallels.com> <20111110184654.GA1006@redhat.com> <20111110185603.GA1757@redhat.com> <4EBCF4E7.4090002@parallels.com> <20111111152532.GA22640@redhat.com> <4EBD461E.1000106@parallels.com> <4EBD4ACB.2070001@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4EBD4ACB.2070001@parallels.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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