From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752630AbXCMKbi (ORCPT ); Tue, 13 Mar 2007 06:31:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753215AbXCMKbi (ORCPT ); Tue, 13 Mar 2007 06:31:38 -0400 Received: from mx2.suse.de ([195.135.220.15]:54135 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752630AbXCMKbi (ORCPT ); Tue, 13 Mar 2007 06:31:38 -0400 Date: Tue, 13 Mar 2007 11:31:34 +0100 From: Andrea Arcangeli To: Nick Piggin Cc: Anton Blanchard , Rik van Riel , Lorenzo Allegrucci , linux-kernel@vger.kernel.org, Ingo Molnar , Suparna Bhattacharya , Jens Axboe Subject: Re: SMP performance degradation with sysbench Message-ID: <20070313103134.GF8992@v2.random> References: <1172425476.5489.11.camel@odyssey.lan> <45E21FEC.9060605@redhat.com> <45E2E244.8040009@yahoo.com.au> <20070312220042.GA807@kryten> <45F63266.1080509@yahoo.com.au> <20070313094559.GC8992@v2.random> <45F67796.4040508@yahoo.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <45F67796.4040508@yahoo.com.au> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 13, 2007 at 09:06:14PM +1100, Nick Piggin wrote: > Well ignoring the HT issue, I was seeing lots of idle time simply > because userspace could not keep up enough load to the scheduler. > There simply were fewer runnable tasks than CPU cores. When you said idle I thought idle and not waiting for I/O. Waiting for I/O would be hardly a kernel issue ;). If they're not waiting for I/O and they're not scheduling in userland with nanosleep/pause, the cpu shouldn't go idle. Even if they're calling sched_yield in a loop the cpu should account for zero idle time as far as I can tell.