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=-2.4 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT 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 B4BA2FD21E1 for ; Mon, 30 Jul 2018 15:59:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 635A2205C9 for ; Mon, 30 Jul 2018 15:59:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ERsNxviW" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 635A2205C9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org 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 S1727094AbeG3RfN (ORCPT ); Mon, 30 Jul 2018 13:35:13 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:42776 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726661AbeG3RfM (ORCPT ); Mon, 30 Jul 2018 13:35:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=JhUGT8sN1qnvQgwPcAGp95UI9VXlMTxKP19lrE71egg=; b=ERsNxviW6dodssOHkG98471HCn g2inBLUt0s27o+JlXhTEftTY1k/G85PyUglbq4T3m6zb/Y4/LonVS3IcqvLV6o7f0PisL5ft4hNs0 ADg4mmAMHUzY7yEKjM9tI/70mV0vM0ndvudZIrediVniAeAVSj0d/PfCfJwtlRSYNTcrbXiyg8BfY XOpEE8ysM9XC47UDEcJ8sDimyWVIoYBoslRSiAXjdHys2hNMskjE3gKWkszFOWfnAMbGu5EnhRIRC MxpxNA1C7ZwS3i2oh8rbUlYHCBW2s4CXtfoj6l3WQOVl2oQkCyFZHzMFxo6MYP9mrWI30pChB7UgY hzwXYRzQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fkAa7-0003y6-AA; Mon, 30 Jul 2018 15:59:35 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 15B742026873D; Mon, 30 Jul 2018 17:59:33 +0200 (CEST) Date: Mon, 30 Jul 2018 17:59:33 +0200 From: Peter Zijlstra To: "weiqi (C)" Cc: linux-kernel@vger.kernel.org, Zhanghailiang Subject: Re: [Question] load balance move tasks not suitable ? Message-ID: <20180730155933.GK2494@hirez.programming.kicks-ass.net> References: <6e782fa5-de1d-93a9-ed11-5b43b65b20c9@huawei.com> <20180730125606.GP2476@hirez.programming.kicks-ass.net> <8513a5c1-2067-cdf6-285f-3fb422274c05@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8513a5c1-2067-cdf6-285f-3fb422274c05@huawei.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail? On Mon, Jul 30, 2018 at 09:42:27PM +0800, weiqi (C) wrote: > 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. imbalance is how much we should move to get in balance. So if we move 1 imbalance we'll end up being just right. If we move 1.5 we end up slightly better then before, but imbalanced the other way. If we move 2 imbalance, we're exactly where we were, just the other way around. > 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. We might not move anything and not improve even if we could.