From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 28BBAC38A24 for ; Thu, 7 May 2020 15:54:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0DED720659 for ; Thu, 7 May 2020 15:54:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727092AbgEGPy1 (ORCPT ); Thu, 7 May 2020 11:54:27 -0400 Received: from outbound-smtp38.blacknight.com ([46.22.139.221]:47513 "EHLO outbound-smtp38.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726451AbgEGPy1 (ORCPT ); Thu, 7 May 2020 11:54:27 -0400 Received: from mail.blacknight.com (pemlinmail02.blacknight.ie [81.17.254.11]) by outbound-smtp38.blacknight.com (Postfix) with ESMTPS id 42AB81A36 for ; Thu, 7 May 2020 16:54:25 +0100 (IST) Received: (qmail 4187 invoked from network); 7 May 2020 15:54:25 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.18.57]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 7 May 2020 15:54:24 -0000 Date: Thu, 7 May 2020 16:54:22 +0100 From: Mel Gorman To: Jirka Hladky Cc: Phil Auld , Peter Zijlstra , Ingo Molnar , Vincent Guittot , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Ben Segall , Valentin Schneider , Hillf Danton , LKML , Douglas Shakshober , Waiman Long , Joe Mario , Bill Gray Subject: Re: [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v6 Message-ID: <20200507155422.GD3758@techsingularity.net> References: <20200312155640.GX3818@techsingularity.net> <20200312214736.GA3818@techsingularity.net> <20200320152251.GC3818@techsingularity.net> <20200320163843.GD3818@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 07, 2020 at 05:24:17PM +0200, Jirka Hladky wrote: > Hi Mel, > > > > Yes, it's indeed OMP. With low threads count, I mean up to 2x number of > > > NUMA nodes (8 threads on 4 NUMA node servers, 16 threads on 8 NUMA node > > > servers). > > > > Ok, so we know it's within the imbalance threshold where a NUMA node can > > be left idle. > > we have discussed today with my colleagues the performance drop for > some workloads for low threads counts (roughly up to 2x number of NUMA > nodes). We are worried that it can be a severe issue for some use > cases, which require a full memory bandwidth even when only part of > CPUs is used. > > We understand that scheduler cannot distinguish this type of workload > from others automatically. However, there was an idea for a * new > kernel tunable to control the imbalance threshold *. Based on the > purpose of the server, users could set this tunable. See the tuned > project, which allows creating performance profiles [1]. > I'm not completely opposed to it but given that the setting is global, I imagine it could have other consequences if two applications ran at different times have different requirements. Given that it's OMP, I would have imagined that an application that really cared about this would specify what was needed using OMP_PLACES. Why would someone prefer kernel tuning or a tuned profile over OMP_PLACES? After all, it requires specific knowledge of the application even to know that a particular tuned profile is needed. -- Mel Gorman SUSE Labs