From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964815AbWIIT4m (ORCPT ); Sat, 9 Sep 2006 15:56:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751383AbWIIT4m (ORCPT ); Sat, 9 Sep 2006 15:56:42 -0400 Received: from omx2-ext.sgi.com ([192.48.171.19]:52875 "EHLO omx2.sgi.com") by vger.kernel.org with ESMTP id S1751382AbWIIT4k (ORCPT ); Sat, 9 Sep 2006 15:56:40 -0400 Date: Sat, 9 Sep 2006 12:56:16 -0700 (PDT) From: Christoph Lameter To: "Siddha, Suresh B" cc: akpm@osdl.org, linux-kernel@vger.kernel.org, npiggin@suse.de, mingo@elte.hu Subject: Re: [PATCH] Fix longstanding load balancing bug in the scheduler. In-Reply-To: Message-ID: References: <20060908103529.A9121@unix-os.sc.intel.com> <20060908130028.A9446@unix-os.sc.intel.com> <20060908170352.C9446@unix-os.sc.intel.com> 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 Fri, 8 Sep 2006, Christoph Lameter wrote: > > one or more, it is unnecessary for the common case. > > The common case is an arch with much less cpus. The maxinum on i386 > f.e. is 255 meaning 8 bytes. That fits in the cacheline that is already > used for the stack frame of the calling function. Ughh. Wrong. 255 cpus require 32 bytes. System rarely have that much. If you configure a kernel with less than 32 cpus then this will be one word on the stack. Also note that the patch restricts the search to online cpus. The scheduler will check offline cpus without this patch. That may actually result in speed improvements since the cachelines from offline cpus are no longer brought in during the search for the busiest group / cpu.