From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031079AbeBNOw4 (ORCPT ); Wed, 14 Feb 2018 09:52:56 -0500 Received: from mail.kernel.org ([198.145.29.99]:52318 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030675AbeBNOwy (ORCPT ); Wed, 14 Feb 2018 09:52:54 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 20D6420671 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: Wed, 14 Feb 2018 15:52:50 +0100 From: Frederic Weisbecker To: Ingo Molnar Cc: LKML , Peter Zijlstra , Chris Metcalf , Thomas Gleixner , Luiz Capitulino , Christoph Lameter , "Paul E . McKenney" , Wanpeng Li , Mike Galbraith , Rik van Riel Subject: Re: [PATCH 6/6] sched/isolation: Tick offload documentation Message-ID: <20180214145248.GA2456@lerouge> References: <1518112779-30196-1-git-send-email-frederic@kernel.org> <1518112779-30196-7-git-send-email-frederic@kernel.org> <20180209070649.kuk3dbwsycnqugsd@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180209070649.kuk3dbwsycnqugsd@gmail.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 Fri, Feb 09, 2018 at 08:06:49AM +0100, Ingo Molnar wrote: > > * Frederic Weisbecker wrote: > > > Update the documentation to reflect the 1Hz tick offload changes. > > > > Signed-off-by: Frederic Weisbecker > > Cc: Chris Metcalf > > Cc: Christoph Lameter > > Cc: Luiz Capitulino > > Cc: Mike Galbraith > > Cc: Paul E. McKenney > > Cc: Peter Zijlstra > > Cc: Rik van Riel > > Cc: Thomas Gleixner > > Cc: Wanpeng Li > > Cc: Ingo Molnar > > --- > > Documentation/admin-guide/kernel-parameters.txt | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > index 39ac9d4..c851e41 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -1762,7 +1762,11 @@ > > specified in the flag list (default: domain): > > > > nohz > > - Disable the tick when a single task runs. > > + Disable the tick when a single task runs. A residual 1Hz > > + tick is offloaded to workqueues that you need to affine > > + to housekeeping through the sysfs file > > + /sys/devices/virtual/workqueue/cpumask or using the below > > + domain flag. > > This is pretty ambiguous and somewhat confusing, I'd suggest something like: > > nohz > Disable the tick when a single task runs. > > A residual 1Hz tick is offloaded to workqueues, which you > need to affine to housekeeping through the global > workqueue's affinity configured via the > /sys/devices/virtual/workqueue/cpumask sysfs file, or > by using the 'domain' flag described below. > > NOTE: by default the global workqueue runs on all CPUs, > so to protect individual CPUs the 'cpumask' file has to > be configured manually after bootup. > > Assuming what I wrote is correct - the CPU isolation config space is pretty > confusing all around and should be made a lot more human friendly ... That's right. In fact "nohz_full=" affines the workqueues and it involves much more: unbound timers affinity, RCU threads, etc... So "nohz_full=" is the friendly interface as it does all in one. Now the use of "isolcpus=" is supposed to be more finegrained and allow for more control. Ideally I would like to have an "unbound" flag which affines all these unbound works. And why not a "per_cpu" flag to disable or offload per cpu work such as watchdog. So we would only need to do: isolcpus=nohz,unbound,per_cpu Or even just: isolcpus=all But before extending further isolcpus=, I would like to make sure I can make it mutable later through cpusets. So this is work in progress. Thanks.