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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 7F158C5519F for ; Tue, 17 Nov 2020 14:44:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3827F2222E for ; Tue, 17 Nov 2020 14:44:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728937AbgKQOop (ORCPT ); Tue, 17 Nov 2020 09:44:45 -0500 Received: from outbound-smtp21.blacknight.com ([81.17.249.41]:47110 "EHLO outbound-smtp21.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728740AbgKQOom (ORCPT ); Tue, 17 Nov 2020 09:44:42 -0500 Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp21.blacknight.com (Postfix) with ESMTPS id 58372CCC42 for ; Tue, 17 Nov 2020 14:44:40 +0000 (GMT) Received: (qmail 16539 invoked from network); 17 Nov 2020 14:44:40 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 17 Nov 2020 14:44:40 -0000 Date: Tue, 17 Nov 2020 14:44:38 +0000 From: Mel Gorman To: Vincent Guittot Cc: LKML , Ingo Molnar , Peter Zijlstra , Valentin Schneider , Juri Lelli Subject: Re: [PATCH 2/3] sched/numa: Allow a floating imbalance between NUMA nodes Message-ID: <20201117144438.GA3371@techsingularity.net> References: <20201117134222.31482-1-mgorman@techsingularity.net> <20201117134222.31482-3-mgorman@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) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 17, 2020 at 03:24:56PM +0100, Vincent Guittot wrote: > On Tue, 17 Nov 2020 at 14:42, Mel Gorman wrote: > > > > Currently, an imbalance is only allowed when a destination node > > is almost completely idle. This solved one basic class of problems > > and was the cautious approach. > > > > This patch revisits the possibility that NUMA nodes can be imbalanced > > until 25% of the CPUs are occupied. The reasoning behind 25% is somewhat > > superficial -- it's half the cores when HT is enabled. At higher > > utilisations, balancing should continue as normal and keep things even > > until scheduler domains are fully busy or over utilised. > > This reminds me previous discussions on the same topic: how much > imbalance is allowed that will not screw up the bandwidth of the node > I'm worried that there is no topology insight in the decision like > hyperthreading, or number of cpus in the LLC > We still don't have a good answer for that. It could be a tunable I guess but it would be horrible to tune properly. -- Mel Gorman SUSE Labs