From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751507AbbDEFcG (ORCPT ); Sun, 5 Apr 2015 01:32:06 -0400 Received: from mail-wi0-f179.google.com ([209.85.212.179]:36602 "EHLO mail-wi0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750759AbbDEFcC (ORCPT ); Sun, 5 Apr 2015 01:32:02 -0400 Message-ID: <1428211919.2324.23.camel@gmail.com> Subject: Re: [PATCH RFC] nohz,blk-mq: do not create blk-mq workqueues on nohz dedicated CPUs From: Mike Galbraith To: Rik van Riel Cc: axboe@kernel.org, fweisbec@redhat.com, mingo@kernel.org, linux-kernel@vger.kernel.org, lcapitulino@redhat.com, mtosatti@redhat.com Date: Sun, 05 Apr 2015 07:31:59 +0200 In-Reply-To: <20150331102726.076a6860@annuminas.surriel.com> References: <20150331102726.076a6860@annuminas.surriel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.0 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2015-03-31 at 10:27 -0400, Rik van Riel wrote: > CPUs with nohz_full do not want disruption from timer interrupts, > or other random system things. This includes block mq work. > > There is another issue with block mq vs. realtime tasks that run > 100% of the time, which is not uncommon on systems that have CPUs > dedicated to real time use with isolcpus= and nohz_full= > > Specifically, on systems like that, a block work item may never > get to run, which could lead to filesystems getting stuck forever. What reason is there to run a compute hog as RT if it's the only task on an isolated core? In an RT kernel, PI may be a reason, but if a task is so critical that it needs bare metal, it had better not be. -Mike