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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 C407E13F6DFF for ; Mon, 30 Jul 2018 13:42:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7FF5420893 for ; Mon, 30 Jul 2018 13:42:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7FF5420893 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com 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 S1726818AbeG3PRs (ORCPT ); Mon, 30 Jul 2018 11:17:48 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:10156 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726530AbeG3PRs (ORCPT ); Mon, 30 Jul 2018 11:17:48 -0400 Received: from DGGEMS405-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 357442B75703D; Mon, 30 Jul 2018 21:42:33 +0800 (CST) Received: from [10.177.98.84] (10.177.98.84) by smtp.huawei.com (10.3.19.205) with Microsoft SMTP Server (TLS) id 14.3.399.0; Mon, 30 Jul 2018 21:42:27 +0800 Subject: Re: [Question] load balance move tasks not suitable ? To: Peter Zijlstra References: <6e782fa5-de1d-93a9-ed11-5b43b65b20c9@huawei.com> <20180730125606.GP2476@hirez.programming.kicks-ass.net> CC: , Zhanghailiang From: "weiqi (C)" Message-ID: <8513a5c1-2067-cdf6-285f-3fb422274c05@huawei.com> Date: Mon, 30 Jul 2018 21:42:27 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20180730125606.GP2476@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.177.98.84] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org in latest linux kernel version, load-balance's detach_tasks() keeps "load/2" behavior: """ if (( load / 2 ) > env->imbalance) goto next; """ It means a task "p", which load is 1.5 times than "env->imbalance" can move from "src_rq" to "dst_rq". after this move, imbalance between "src_rq" and "dst_rq" may larger than before. but if use "load*2" here, It means we can pick a task "p" , which load is half of "env->imbalance"， and after move， "src_rq" and "dst_rq" is balanced. Am I right? 在 2018/7/30 20:56, Peter Zijlstra 写道: > On Mon, Jul 30, 2018 at 08:08:55PM +0800, weiqi (C) wrote: >> Hi Peter, >> >> After Commits 5d6523ebd(sched: Fix load-balance wreckage)， > That's a _6_ year old patch... and I can barely remember last week. > >> The jugement whether imbalance reached changed from twice to one-half. >> >> from >> >> (1) if((load * 2)> rem_load_move) >> goto next; >> >> to >> >> (2) if((load / 2)> env-> load_move) >> goto next; >> >> I'm confused about this change. >> >> "load*2" may be more appropriate, because if a task whose load more than >> env->imbalance is moved from high load cpu to low load cpu, >> >> will make more imbalance. > It basically goes back to what it was before (see 367456c), in that > patch I (inadvertently) replaced (load.weight >> 1) with (load * 2) > instead of (load / 2). > > I'm not entirely sure I can explain that logic at this time. Doing > software archeology on it might clarify where it came from. > . >