From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964964AbXCAMH1 (ORCPT ); Thu, 1 Mar 2007 07:07:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965031AbXCAMH0 (ORCPT ); Thu, 1 Mar 2007 07:07:26 -0500 Received: from mail09.syd.optusnet.com.au ([211.29.132.190]:40655 "EHLO mail09.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964964AbXCAMH0 (ORCPT ); Thu, 1 Mar 2007 07:07:26 -0500 From: Con Kolivas To: tglx@linutronix.de Subject: Re: 2.6.21-rc1: known regressions (v2) (part 2) Date: Thu, 1 Mar 2007 23:05:53 +1100 User-Agent: KMail/1.9.5 Cc: Ingo Molnar , Mike Galbraith , Michal Piotrowski , Adrian Bunk , Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org References: <200703012213.25629.kernel@kolivas.org> <1172748837.11473.53.camel@localhost.localdomain> In-Reply-To: <1172748837.11473.53.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200703012305.53997.kernel@kolivas.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thursday 01 March 2007 22:33, Thomas Gleixner wrote: > On Thu, 2007-03-01 at 22:13 +1100, Con Kolivas wrote: > > > if then there should be a mechanism /in the hardware/ to set the > > > priority of a CPU - and then the hardware could decide how to > > > prioritize between siblings. Doing this in software is really hard. > > > > And that's the depressing part because of course I was interested in that > > as the original approach to the problem (and it was a big problem). When > > I spoke to Intel and AMD (of course to date no SMT AMD chip exists) at > > kernel summit they said it was too hard to implement hardware priorities > > well. Which is real odd since IBM have already done it with Power... > > > > Still I think it has been working fine in software till now, but now it > > has to deal with the added confusion of dynticks, so I already know what > > will happen to it. > > Well, it's not a dyntick problem in the first place. Even w/o dynticks > we go idle with local_softirq_pending(). Dynticks contains an explicit > check for that, which makes it visible. Oops I'm sorry if I made it sound like there's a dynticks problem. That was not my intent and I said as much in an earlier email. Even though I'm finding myself defending code that has already been softly tagged for redundancy, let's be clear here; we're talking about at most a further 70ms delay in scheduling a niced task in the presence of a nice 0 task, which is a reasonable delay for ksoftirqd which we nice the eyeballs out of in mainline. Considering under load our scheduler has been known to cause scheduling delays of 10 seconds I still don't see this as a bug. Dynticks just "points it out to us". -- -ck