From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756937AbaEIPeP (ORCPT ); Fri, 9 May 2014 11:34:15 -0400 Received: from qmta09.emeryville.ca.mail.comcast.net ([76.96.30.96]:37034 "EHLO qmta09.emeryville.ca.mail.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756922AbaEIP2c (ORCPT ); Fri, 9 May 2014 11:28:32 -0400 Date: Fri, 9 May 2014 10:28:27 -0500 (CDT) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Thomas Gleixner cc: Andrew Morton , Gilad Ben-Yossef , Tejun Heo , John Stultz , Mike Frysinger , Minchan Kim , Hakan Akkan , Max Krasnyansky , Frederic Weisbecker , "Paul E. McKenney" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, hughd@google.com, viresh.kumar@linaro.org Subject: Re: vmstat: On demand vmstat workers V4 In-Reply-To: Message-ID: References: <20140508142903.c2ef166c95d2b8acd0d7ea7d@linux-foundation.org> Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 9 May 2014, Thomas Gleixner wrote: > > Ok how do I figure out that cpu? I'd rather have a specific cpu that > > never changes. > > I followed the full nohz development only losely, but back then when > all started here at my place with frederic, we had a way to define the > housekeeper cpu. I think we lazily had it hardwired to 0 :) Yes that would be the easiest and simplest. We dedicate cpu 0 to OS services around here anyways. > That probably changed, but I'm sure there is still a way to define a > housekeeper. And we should simply force the timekeeping on that > housekeeper. That comes with the price, that the housekeeper is not > allowed to go deep idle, but I bet that in HPC scenarios this does not > matter at all simply because the whole machine is under full load. Excellent. Yes. Good. > > > > The vmstat kworker thread checks every 2 seconds if there are vmstat > > updates that need to be folded into the global statistics. This is not > > necessary if the application is running and no OS services are being used. > > Thus we could switch off vmstat updates and avoid taking the processor > > away from the application. > > > > This has also been noted by multiple other people at was brought up at the > > mm summit by others who noted the same issues. > > I understand why you want to get this done by a housekeeper, I just > did not understand why we need this whole move it around business is > required. This came about because of another objection against having it simply fixed to a processor. After all that processor may be disabled etc etc.