From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760006AbXG2DBi (ORCPT ); Sat, 28 Jul 2007 23:01:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759587AbXG2DBa (ORCPT ); Sat, 28 Jul 2007 23:01:30 -0400 Received: from mx1.redhat.com ([66.187.233.31]:49681 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759118AbXG2DB3 (ORCPT ); Sat, 28 Jul 2007 23:01:29 -0400 Message-ID: <46AC02FA.8060303@redhat.com> Date: Sat, 28 Jul 2007 23:01:14 -0400 From: Chris Snook User-Agent: Thunderbird 1.5.0.12 (Macintosh/20070509) MIME-Version: 1.0 To: Tong Li CC: Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: [RFC] scheduler: improve SMP fairness in CFS References: <20070725110159.GA15076@elte.hu> <20070725120358.GA30755@elte.hu> <20070725192442.GC4463@elte.hu> <20070726213154.GA26569@elte.hu> <1185487225.3122.11.camel@tongli.jf.intel.com> <46AA287D.8070200@redhat.com> <46AA8171.2060400@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Tong Li wrote: > Without the global locking, the global synchronization here is simply > ping-ponging a cache line once of while. This doesn't look expensive to > me, but if it does after benchmarking, adjusting sysctl_base_round_slice > can reduce the ping-pong frequency. There might also be a smart > implementation that can alleviate this problem. Scaling it proportionally to migration cost and log2(cpus) should suffice. > I don't understand why quantizing CPU time is a bad thing. Could you > educate me on this? It depends on how precisely you do it. We save a lot of power going tickless. If round expiration is re-introducing ticks on idle CPUs, we could waste a lot of power. Hardware is getting even more aggressive about power saving, to the point of allowing individual cores to be completely powered off when idle. We need to make sure the scheduler doesn't interfere with power management. -- Chris