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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_GIT autolearn=ham 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 09D49C4321E for ; Fri, 7 Sep 2018 10:12:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BC4432083D for ; Fri, 7 Sep 2018 10:12:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BC4432083D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=techsingularity.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727785AbeIGOv4 (ORCPT ); Fri, 7 Sep 2018 10:51:56 -0400 Received: from outbound-smtp13.blacknight.com ([46.22.139.230]:44065 "EHLO outbound-smtp13.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725942AbeIGOv4 (ORCPT ); Fri, 7 Sep 2018 10:51:56 -0400 Received: from mail.blacknight.com (unknown [81.17.254.17]) by outbound-smtp13.blacknight.com (Postfix) with ESMTPS id 650111C31F7 for ; Fri, 7 Sep 2018 11:11:40 +0100 (IST) Received: (qmail 19888 invoked from network); 7 Sep 2018 10:11:40 -0000 Received: from unknown (HELO stampy.163woodhaven.lan) (mgorman@techsingularity.net@[37.228.229.88]) by 81.17.254.9 with ESMTPA; 7 Sep 2018 10:11:40 -0000 From: Mel Gorman To: Srikar Dronamraju , Peter Zijlstra Cc: Ingo Molnar , Rik van Riel , LKML , Mel Gorman Subject: [PATCH 0/4] Follow-up fixes for v4.19-rc1 NUMA balancing Date: Fri, 7 Sep 2018 11:11:35 +0100 Message-Id: <20180907101139.20760-1-mgorman@techsingularity.net> X-Mailer: git-send-email 2.16.4 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Srikar had an automatic NUMA balancing series merged during the 4.19 window and there some issues I missed during review that this series addresses. Patches 1-2 are simply removing redundant code and calculations that are never used. Patch 3 makes the observation that we can call select_idle_sibling during NUMA placement several times for each idle CPU on a socket. The patch stops the search on the first idle CPU. While there is the risk that parallel callers will stack on the same idle CPU, the current code has the same problem. Patch 4 is the one that needs the most examination. I believe intent of load_too_imbalanced was to stop automatic NUMA balancing fighting the load balancer. Unfortunately, when a machine is lightly utilised there are idle CPUs and tasks are allowed to migrate even though the load is imbalanced. In some cases, this limits memory bandwidth and can perform worse even if data locality is fine. The patch corrects the condition. If they pass review, I think it would suggest considering them a fix for 4.19 instead of deferring to 4.20. kernel/sched/fair.c | 35 ++++++++--------------------------- 1 file changed, 8 insertions(+), 27 deletions(-) -- 2.16.4