From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756573Ab3JGSjn (ORCPT ); Mon, 7 Oct 2013 14:39:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48720 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751995Ab3JGSjm (ORCPT ); Mon, 7 Oct 2013 14:39:42 -0400 Message-ID: <5252FFD8.2020800@redhat.com> Date: Mon, 07 Oct 2013 14:39:20 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Mel Gorman CC: Peter Zijlstra , Srikar Dronamraju , Ingo Molnar , Andrea Arcangeli , Johannes Weiner , Linux-MM , LKML Subject: Re: [PATCH 21/63] sched: Update NUMA hinting faults once per scan References: <1381141781-10992-1-git-send-email-mgorman@suse.de> <1381141781-10992-22-git-send-email-mgorman@suse.de> In-Reply-To: <1381141781-10992-22-git-send-email-mgorman@suse.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/07/2013 06:28 AM, Mel Gorman wrote: > NUMA hinting fault counts and placement decisions are both recorded in the > same array which distorts the samples in an unpredictable fashion. The values > linearly accumulate during the scan and then decay creating a sawtooth-like > pattern in the per-node counts. It also means that placement decisions are > time sensitive. At best it means that it is very difficult to state that > the buffer holds a decaying average of past faulting behaviour. At worst, > it can confuse the load balancer if it sees one node with an artifically high > count due to very recent faulting activity and may create a bouncing effect. > > This patch adds a second array. numa_faults stores the historical data > which is used for placement decisions. numa_faults_buffer holds the > fault activity during the current scan window. When the scan completes, > numa_faults decays and the values from numa_faults_buffer are copied > across. > > Signed-off-by: Mel Gorman Reviewed-by: Rik van Riel -- All rights reversed