From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754057AbeARDEt (ORCPT ); Wed, 17 Jan 2018 22:04:49 -0500 Received: from mail.kernel.org ([198.145.29.99]:59100 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753296AbeARDEq (ORCPT ); Wed, 17 Jan 2018 22:04:46 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3B9E021742 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=frederic@kernel.org Date: Thu, 18 Jan 2018 04:04:43 +0100 From: Frederic Weisbecker To: Luiz Capitulino 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: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180117123801.11f41f99@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanks!