Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 4 Oct 2001 19:50:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 4 Oct 2001 19:50:22 -0400 Received: from neon-gw-l3.transmeta.com ([63.209.4.196]:44039 "EHLO neon-gw.transmeta.com") by vger.kernel.org with ESMTP id ; Thu, 4 Oct 2001 19:50:10 -0400 Date: Thu, 4 Oct 2001 16:50:13 -0700 (PDT) From: Linus Torvalds To: Mike Kravetz cc: Subject: Re: Context switch times In-Reply-To: <20011004164102.E1245@w-mikek2.des.beaverton.ibm.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 4 Oct 2001, Mike Kravetz wrote: > On Thu, Oct 04, 2001 at 10:42:37PM +0000, Linus Torvalds wrote: > > Could we try to hit just two? Probably, but it doesn't really matter, > > though: to make the lmbench scheduler benchmark go at full speed, you > > want to limit it to _one_ CPU, which is not sensible in real-life > > situations. > > Can you clarify? I agree that tuning the system for the best LMbench > performance is not a good thing to do! However, in general on an > 8 CPU system with only 2 'active' tasks I would think limiting the > tasks to 2 CPUs would be desirable for cache effects. Yes, limiting to 2 CPU's probably gets better cache behaviour, and it might be worth looking into why it doesn't. The CPU affinity _should_ prioritize it down to two, but I haven't thought through your theory about IPI latency. However, the reason 2.2.x does so well is that in 2.2.x it will stay on _once_ CPU if I remember correctly. We basically tuned the scheduler for lmbench, and not much else. Linus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/