From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030501AbXALGCT (ORCPT ); Fri, 12 Jan 2007 01:02:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161002AbXALGCT (ORCPT ); Fri, 12 Jan 2007 01:02:19 -0500 Received: from ns2.suse.de ([195.135.220.15]:39243 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030501AbXALGCT (ORCPT ); Fri, 12 Jan 2007 01:02:19 -0500 Date: Fri, 12 Jan 2007 07:02:13 +0100 From: Nick Piggin To: Andrew Morton , Ingo Molnar , Linux Kernel Mailing List Subject: [patch] sched: avoid div in rebalance_tick Message-ID: <20070112060213.GB28611@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Just noticed this while looking at a bug. -- Avoid an expensive integer divide 3 times per CPU per tick. Signed-off-by: Nick Piggin Index: linux-2.6/kernel/sched.c =================================================================== --- linux-2.6.orig/kernel/sched.c +++ linux-2.6/kernel/sched.c @@ -2887,13 +2887,14 @@ static void active_load_balance(struct r static void update_load(struct rq *this_rq) { unsigned long this_load; - int i, scale; + int i; this_load = this_rq->raw_weighted_load; /* Update our load: */ - for (i = 0, scale = 1; i < 3; i++, scale <<= 1) { + for (i = 0; i < 3; i++) { unsigned long old_load, new_load; + int scale; old_load = this_rq->cpu_load[i]; new_load = this_load; @@ -2902,9 +2903,11 @@ static void update_load(struct rq *this_ * prevents us from getting stuck on 9 if the load is 10, for * example. */ + scale = 1 << i; if (new_load > old_load) new_load += scale-1; - this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) / scale; + this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) + >> i; /* (divide by 'scale') */ } }