Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753825AbbDBOWG (ORCPT ); Thu, 2 Apr 2015 10:22:06 -0400 Received: from resqmta-po-12v.sys.comcast.net ([96.114.154.171]:56961 "EHLO resqmta-po-12v.sys.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753769AbbDBOV7 (ORCPT ); Thu, 2 Apr 2015 10:21:59 -0400 X-Greylist: delayed 490 seconds by postgrey-1.27 at vger.kernel.org; Thu, 02 Apr 2015 10:21:59 EDT Date: Thu, 2 Apr 2015 09:13:03 -0500 (CDT) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Chris Metcalf cc: Andrew Morton , Don Zickus , Andrew Jones , chai wen , Ingo Molnar , Ulrich Obergfell , Fabian Frederick , Aaron Tomlin , Ben Zhang , Frederic Weisbecker , Gilad Ben-Yossef , Steven Rostedt , open list Subject: Re: [PATCH] watchdog: nohz: don't run watchdog on nohz_full cores In-Reply-To: <551AE9D0.5090103@ezchip.com> Message-ID: References: <1427741465-15747-1-git-send-email-cmetcalf@ezchip.com> <551AE9D0.5090103@ezchip.com> Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1478 Lines: 30 On Tue, 31 Mar 2015, Chris Metcalf wrote: > This may come back to a question of just why one believes that > nohz_full is a good thing in the first place. For folks that are doing > it just to improve performance, power, etc, generally, it may not > matter much whether the watchdog ticks occasionally. But for folks > who are doing it to establish cores that are run completely tick-free > for days on end so they can help process 100 Gb packet streams > and never drop a packet, the calculus is a little different. My bias > is to say that once you've tagged a core as nohz_full, you never want > to run the watchdog on it. But it's worth supporting multiple uses > of nohz_full, certainly. Completely tick-free is some ideal. What is really needed is to make it rare. We do not want to cripple the cores that have a reduced tick. If someone configures a watchdog to run every X seconds on a NOHZ core then he should get the tick every X seconds because that is what he requested. If someone else do not want the watchdog to run then they are willing to accept the limitations in debugging that come with it. For that to work we need to have a way to configure this. Maybe allow the specification of a cpumask somewhere? -- 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/