Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755597AbaGSRb2 (ORCPT ); Sat, 19 Jul 2014 13:31:28 -0400 Received: from mail-qc0-f175.google.com ([209.85.216.175]:47095 "EHLO mail-qc0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751175AbaGSRb1 (ORCPT ); Sat, 19 Jul 2014 13:31:27 -0400 Date: Sat, 19 Jul 2014 13:31:25 -0400 (EDT) From: Nicolas Pitre To: Frederic Weisbecker cc: LKML , Ingo Molnar , "Paul E. McKenney" , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Viresh Kumar Subject: Re: [PATCH 07/10] nohz: Enforce timekeeping on CPU 0 In-Reply-To: <1405730661-9355-8-git-send-email-fweisbec@gmail.com> Message-ID: References: <1405730661-9355-1-git-send-email-fweisbec@gmail.com> <1405730661-9355-8-git-send-email-fweisbec@gmail.com> User-Agent: Alpine 2.11 (LFD 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 19 Jul 2014, Frederic Weisbecker wrote: > The timekeeper gets initialized to the value of the CPU where the > first clockevent device is setup. This works well because the timekeeper > can be any online CPU in most configs. > > Full dynticks has its own requirement though and needs the timekeeper > to always be 0. And this requirement seem to accomodate pretty well with > the above described boot timekeeper setting because the first clockevent > device happens to be initialized, most of the time, on the boot CPU > (which should be CPU 0). This might have been discussed before... but this isn't ARM big.LITTLE friendly at all. Could we accommodate for any arbitrary CPU instead of making CPU 0 "special" other than its role as the boot CPU please? It doesn't have to be completely dynamic, but CPU 0 might be a really bad choice for ongoing periodic duties in some configurations. For example, we might highly prefer to do this on CPU 4 for power efficiency reasons once it is online and keep CPU 0 in a deep C-state as much as possible. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/