Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755808AbbHYI3M (ORCPT ); Tue, 25 Aug 2015 04:29:12 -0400 Received: from mail-wi0-f176.google.com ([209.85.212.176]:33459 "EHLO mail-wi0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753396AbbHYI3J (ORCPT ); Tue, 25 Aug 2015 04:29:09 -0400 Date: Tue, 25 Aug 2015 10:29:04 +0200 From: Ingo Molnar To: Frederic Weisbecker Cc: "Paul E. McKenney" , Peter Zijlstra , LKML , Vatika Harlalka , Chris Metcalf , Thomas Gleixner , Preeti U Murthy , Christoph Lameter Subject: Re: [PATCH RESEND] sched/nohz: Affine unpinned timers to housekeepers Message-ID: <20150825082904.GA20562@gmail.com> References: <1439516774-4614-1-git-send-email-fweisbec@gmail.com> <20150823054032.GA28133@gmail.com> <20150823160101.GA11078@linux.vnet.ibm.com> <20150824064412.GA11581@gmail.com> <20150824133559.GA27147@lerouge> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150824133559.GA27147@lerouge> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1282 Lines: 33 * Frederic Weisbecker wrote: > On Mon, Aug 24, 2015 at 08:44:12AM +0200, Ingo Molnar wrote: > > 2) > > > > What happens if the boot CPU is offlined? (under CONFIG_BOOTPARAM_HOTPLUG_CPU0=y) > > > > I don't see CPU hotplug callbacks fixing up the housekeeping_mask if the boot CPU > > is offlined. > > We have tick_nohz_cpu_down_callback() which makes sure that the timekeeper, which > is the boot CPU in nohz full, never gets offlined. That solution really sucks - it essentially regresses a feature the user explicitly asked for! I also see no way for the user to migrate the timekeeping functionality over to another CPU without rebooting. If this is the last timekeeping CPU then it should migrate the timekeeping functionality to another CPU, and perhaps printk a warning if all other CPUs are nohz-full and we have to mark one of them as the timekeeper. Also, the nohz-full and timekeeper functionality should not be a boot parameter only thing, but should be runtime configurable. Thanks, Ingo -- 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/