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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, URIBL_BLOCKED,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 78CD0C04ABB for ; Tue, 11 Sep 2018 11:31:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 11BED2088F for ; Tue, 11 Sep 2018 11:31:08 +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="FFuUNNMQ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 11BED2088F 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 S1727670AbeIKQaA (ORCPT ); Tue, 11 Sep 2018 12:30:00 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:57310 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726563AbeIKQaA (ORCPT ); Tue, 11 Sep 2018 12:30:00 -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-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding: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=yyY0flhhFjbhGkEJ7erSnfcjQb0peFcvXjjtaJS7CWY=; b=FFuUNNMQILTDHsWih2SDILTB7 kVOP7Gk2vViwa7WKwkAh9VdMKoTsqtqWtbb6aKuLehjBvAt+ICtnehnAPxB6MQZo4mLJ97hDwHY/d TlED+ZHeSdP19MsR/Oiri4Njcru4n1YMQeH3ESib7GsRdM3JYuZQGGfz86luNsGejb9YQwvjT5bQv RVt2n7Pwl4tEGmgDwQrl7/IwAPp6YSmibKhRM5DG+o2ikFjGhRRYduYYYFNGcKUtnGpca0x08G4ar l+62UKDQZSGssB1VC3ABosDuCKeh5whg5+dU/wwHfJLit6JVq+U/jc/NzYgwWmGJBsBYOev2/gANL C72qCvNxg==; 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 1fzgsm-0003nV-QG; Tue, 11 Sep 2018 11:31:00 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 91E252057F82F; Tue, 11 Sep 2018 13:30:58 +0200 (CEST) Date: Tue, 11 Sep 2018 13:30:58 +0200 From: Peter Zijlstra To: Ingo Molnar Cc: Dietmar Eggemann , Ingo Molnar , Fengguang Wu , Li Zhijian , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched/fair: Disable LB_BIAS by default Message-ID: <20180911113058.GQ24106@hirez.programming.kicks-ass.net> References: <20180809135753.21077-1-dietmar.eggemann@arm.com> <20180910141205.GM24106@hirez.programming.kicks-ass.net> <20180911062249.GD72017@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180911062249.GD72017@gmail.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 On Tue, Sep 11, 2018 at 08:22:49AM +0200, Ingo Molnar wrote: > > * Peter Zijlstra wrote: > > > On Thu, Aug 09, 2018 at 02:57:53PM +0100, Dietmar Eggemann wrote: > > > LB_BIAS allows the adjustment on how conservative load should be > > > balanced. > > > > > It is very likely that LB_BIAS' influence on load balancing can be > > > neglected (see test results below). This is further supported by: > > > > > > (1) Weighted CPU load today is by itself a decayed average value (PELT) > > > (cfs_rq->avg->runnable_load_avg) and not the instantaneous load > > > (rq->load.weight) it was when LB_BIAS was introduced. > > > > > > (2) Sd imbalance_pct is used for CPU_NEWLY_IDLE and CPU_NOT_IDLE (relate > > > to sd's newidle and busy idx) in find_busiest_group() when comparing > > > busiest and local avg load to make load balancing even more > > > conservative. > > > > > > (3) The sd forkexec and newidle idx are always set to 0 so there is no > > > adjustment on how conservatively load balancing is done here. > > > > > > (4) Affine wakeup based on weight (wake_affine_weight()) will not be > > > impacted since the sd wake idx is always set to 0. > > > > > > Let's disable LB_BIAS by default for a few kernel releases to make sure > > > that no workload and no scheduler topology is affected. The benefit of > > > being able to remove the LB_BIAS dependency from source_load() and > > > target_load() is that the entire rq->cpu_load[idx] code could be removed > > > in this case. > > > > Certainly worth a try; as I've written somewhere in a comment; it would > > be very nice to get rid of that load tracking crud. > > > > And it is trivial to revert if something does show up. > > > > Ingo, what do you think? > > Ack, I'm very much in favor of reducing complexity. OK, I've queued it up.