From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932579Ab2JKINi (ORCPT ); Thu, 11 Oct 2012 04:13:38 -0400 Received: from mailout-de.gmx.net ([213.165.64.22]:51711 "HELO mailout-de.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1756263Ab2JKINe (ORCPT ); Thu, 11 Oct 2012 04:13:34 -0400 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX18M58Vpxv8MZ78OT/sn2gsZZrLhl3MF6EJbn7aR8T SUDj8BXi+ieMD7 Message-ID: <1349943207.6989.77.camel@marge.simpson.net> Subject: Re: Meaningless load? From: Mike Galbraith To: Simon Klinkert Cc: Peter Zijlstra , LKML , mingo@redhat.com, Trond.Myklebust@netapp.com Date: Thu, 11 Oct 2012 10:13:27 +0200 In-Reply-To: <8CCB73B0-34AD-47E2-9379-DB6F02DB35F5@gmail.com> References: <98F2F644-D531-42FE-B080-9561142D71C8@gmail.com> <1349886164.1279.20.camel@twins> <8CCB73B0-34AD-47E2-9379-DB6F02DB35F5@gmail.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 8bit Mime-Version: 1.0 X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2012-10-11 at 09:19 +0200, Simon Klinkert wrote: > On 10.10.2012, at 18:22, Peter Zijlstra wrote: > > > On Wed, 2012-10-10 at 17:44 +0200, Simon Klinkert wrote: > >> I'm just wondering if the 'load' is really meaningful in this > >> scenario. The machine is the whole time fully responsive and looks > >> fine to me but maybe I didn't understand correctly what the load > >> should mean. Is there any sensible interpretation of the load? > > > > I'll leave meaningful aside, but uninterruptible (D state) is part > of > > how the load thing is defined, so your 500 result is correct. > > Yes, the calculation of the load is correct but I still don't know how > I should interpret the load… > > On 11.10.2012, at 06:02, Mike Galbraith wrote: > > > Makes perfect sense to me. Work _is_ stack this high. We don't and > > can't know whether the mountain is made of popcorn balls or > boulders. > > That's the point. Afaik the D state never represents 'work'. These > processes are waiting for something. Yeah, the whole pile is waiting, but they're not idle. There are N tasks pointed at CPUs. > > Let's say we have 10,000 processes in the D state (and thus a load of > ~10,000) doing nothing. What should the load tell me? The machine is > under fire? There is nothing to do? There might be something to do but > the machine doesn't know? They are doing something, just not at the particular instant you see them in D state. D state pushing load through the roof tells you that you have a bottleneck. Whether the bottleneck is a bit of spinning rust or insufficient NR_CPUS doesn't matter much, both are bottlenecks. -Mike