From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org D941360764 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=fail (p=none dis=none) header.from=linux.vnet.ibm.com Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752035AbeFFNrU (ORCPT + 25 others); Wed, 6 Jun 2018 09:47:20 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:57180 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751575AbeFFNrT (ORCPT ); Wed, 6 Jun 2018 09:47:19 -0400 Date: Wed, 6 Jun 2018 06:47:09 -0700 From: Srikar Dronamraju To: Mel Gorman Cc: Ingo Molnar , Peter Zijlstra , LKML , Rik van Riel , Thomas Gleixner Subject: Re: [PATCH 18/19] sched/numa: Reset scan rate whenever task moves across nodes Reply-To: Srikar Dronamraju References: <1528106428-19992-1-git-send-email-srikar@linux.vnet.ibm.com> <1528106428-19992-19-git-send-email-srikar@linux.vnet.ibm.com> <20180605095843.gfanebla26zvq62j@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20180605095843.gfanebla26zvq62j@techsingularity.net> User-Agent: Mutt/1.5.24 (2015-08-30) X-TM-AS-GCONF: 00 x-cbid: 18060613-0008-0000-0000-00000244C503 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18060613-0009-0000-0000-000021AAD0E2 Message-Id: <20180606134709.GB20331@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-06-06_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1805220000 definitions=main-1806060160 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Mel Gorman [2018-06-05 10:58:43]: > On Mon, Jun 04, 2018 at 03:30:27PM +0530, Srikar Dronamraju wrote: > > Currently task scan rate is reset when numa balancer migrates the task > > to a different node. If numa balancer initiates a swap, reset is only > > applicable to the task that initiates the swap. Similarly no scan rate > > reset is done if the task is migrated across nodes by traditional load > > balancer. > > > > Instead move the scan reset to the migrate_task_rq. This ensures the > > task moved out of its preferred node, either gets back to its preferred > > node quickly or finds a new preferred node. Doing so, would be fair to > > all tasks migrating across nodes. > > > > By and large you need to be very careful resetting the scan rate without > a lot of justification and I don't think this is enough. With scan rate > resets, there is a significant risk that system CPU overhead is > increased to do the page table updates and handle the resulting minor > faults. There are cases where tasks can get pulled cross-node very > frequently and we do not want NUMA balancing scanning agressively when > that happens. > I agree with your thoughts here. I will try to see if there are other workloads that benefit from this change. My rational for this change being, because a workload consolidated and slowed down its scanning shouldn't adversely affect it from coming back to its preferred node. > -- > Mel Gorman > SUSE Labs >