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 45446C4321E for ; Mon, 10 Sep 2018 14:12:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EE80B20870 for ; Mon, 10 Sep 2018 14:12:16 +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="Z2hdUhYO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EE80B20870 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 S1728567AbeIJTGb (ORCPT ); Mon, 10 Sep 2018 15:06:31 -0400 Received: from merlin.infradead.org ([205.233.59.134]:49440 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728110AbeIJTGb (ORCPT ); Mon, 10 Sep 2018 15:06:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=armGffEA1/M7pRn3Mqd4oa4RAnQ93pcaX/gQ46mjXeI=; b=Z2hdUhYOl6jZJpeudWjSrwWrW AfCUMN66T2nPAjEyMl4RKvHALCPIsPrHYkOWOq3VxZhXUDdMHzrByPDg6tYmTRV7pRd0CcZo47jVl b102Cd6NFLsonGekO+JuPexLwyJtTkYlvGoBdsgYYatHh1oGEmLgxCFBl8fXBNjRbFSmdQZIAcG5d H5LbET/46arpEOFXrzF77yWeZ/yUVXkBvkomEOanhOj9eU8iYdp7JQiiSEJ4LXHYQhkEOXpANb3pN yZy8N0PCMp8yFpz7DEy/zdairDjjU5EQKR1OMI44Ve5K2+9JR0FdWl2Vq02N1yQlau5HYFwi4Cs2M U+29e/6nA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fzMv9-0001Uf-R8; Mon, 10 Sep 2018 14:12:08 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2EDF6202C1A02; Mon, 10 Sep 2018 16:12:05 +0200 (CEST) Date: Mon, 10 Sep 2018 16:12:05 +0200 From: Peter Zijlstra To: Dietmar Eggemann Cc: Ingo Molnar , Fengguang Wu , Li Zhijian , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched/fair: Disable LB_BIAS by default Message-ID: <20180910141205.GM24106@hirez.programming.kicks-ass.net> References: <20180809135753.21077-1-dietmar.eggemann@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180809135753.21077-1-dietmar.eggemann@arm.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 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? > Signed-off-by: Dietmar Eggemann > --- > kernel/sched/features.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/features.h b/kernel/sched/features.h > index 85ae8488039c..858589b83377 100644 > --- a/kernel/sched/features.h > +++ b/kernel/sched/features.h > @@ -39,7 +39,7 @@ SCHED_FEAT(WAKEUP_PREEMPTION, true) > > SCHED_FEAT(HRTICK, false) > SCHED_FEAT(DOUBLE_TICK, false) > -SCHED_FEAT(LB_BIAS, true) > +SCHED_FEAT(LB_BIAS, false) > > /* > * Decrement CPU capacity based on time not spent running tasks > -- > 2.11.0 >