From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756476AbeAROCd (ORCPT ); Thu, 18 Jan 2018 09:02:33 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48274 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756359AbeAROCb (ORCPT ); Thu, 18 Jan 2018 09:02:31 -0500 Date: Thu, 18 Jan 2018 09:02:13 -0500 From: Luiz Capitulino To: Frederic Weisbecker Cc: Ingo Molnar , LKML , Peter Zijlstra , Chris Metcalf , Thomas Gleixner , Christoph Lameter , "Paul E . McKenney" , Wanpeng Li , Mike Galbraith , Rik van Riel Subject: Re: [GIT PULL] isolation: 1Hz residual tick offloading v3 Message-ID: <20180118090213.6a1ec99e@redhat.com> In-Reply-To: <20180118030441.GB20310@lerouge> References: <1515039937-367-1-git-send-email-frederic@kernel.org> <20180112141813.32dcc84d@redhat.com> <20180116154055.GA27042@lerouge> <20180116115211.7fd55c9a@redhat.com> <20180116225126.GA32665@lerouge> <20180117123801.11f41f99@redhat.com> <20180118030441.GB20310@lerouge> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 18 Jan 2018 04:04:43 +0100 Frederic Weisbecker wrote: > On Wed, Jan 17, 2018 at 12:38:01PM -0500, Luiz Capitulino wrote: > > On Tue, 16 Jan 2018 23:51:29 +0100 > > Frederic Weisbecker wrote: > > > > > On Tue, Jan 16, 2018 at 11:52:11AM -0500, Luiz Capitulino wrote: > > > > On Tue, 16 Jan 2018 16:41:00 +0100 > > > > Frederic Weisbecker wrote: > > > > > So isolcpus= is now the place where we control the isolation features > > > > > and nohz is one of them. > > > > > > > > That's the part I'm not very sure about. We've been advising users to > > > > move away from isolcpus= when possible, but this very wanted nohz_offload > > > > feature will force everyone back to using isolcpus= again. > > > > > > Note "isolcpus=nohz" only implies nohz. You need to add "domain" to get > > > the behaviour that you've been advising users against. We are simply > > > reusing a kernel parameter that was abandoned to now control the isolation > > > features that were disorganized and opaque behind nohz. > > > > > > > > > > > I have the impression this series is trying to solve two problems: > > > > > > > > 1. How (and where) we control the various isolation features in the > > > > kernel > > > > > > No, that has already been done in the previous merge window. We have a > > > dedicated isolation subsystem now (kernel/sched/isolation.c) and > > > an interface to control all these isolation features that were abusively implied > > > by nohz. The initial plan was to introduce "cpu_isolation=" but it looked too much like > > > "isolcpus=". Then in fact, why not using "isolcpus=" and give it a second life. > > > And there we are. > > > > OK, I get it now. But then series has to un-deprecate isolcpus= otherwise > > it doesn't make sense to use it. > > Good point. Also I think you convinced me toward just applying that tick offload > on the existing nohz kernel parameter right away, that is, to both existing "nohz_full=" > and "isolcpus=nohz". > > After all that tick offload is an implementation detail. > > Like you said if people complain about a regression, we can still fix it > with a new option. But eventually I doubt this will be needed. > > I'll respin with that. Exciting times! Btw, I do have this problem where I have a hog app on an isolated core with isolcpus=nohz_offload,domain,... and I see top -d1 going from 100% to 0% and then back from 0% to 100% every few seconds or so. I'll debug it when you post the next version.