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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 787ECC47095 for ; Wed, 9 Jun 2021 07:12:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5A4B561352 for ; Wed, 9 Jun 2021 07:12:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237079AbhFIHOM (ORCPT ); Wed, 9 Jun 2021 03:14:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54182 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237057AbhFIHOI (ORCPT ); Wed, 9 Jun 2021 03:14:08 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 465E0C06178B for ; Wed, 9 Jun 2021 00:12:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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; bh=76BUpwV+9faalMya9WgMjsJtA0lRIce1TlADEejtRzY=; b=D1aIQkcMtuo1155owLsijrc7RO VHjKah6STnsJwFRjKyYnI+ScMo1McyrPd//3gjkQnPy9cFUtlzfaLvnN1rqDtBAF7CidIaMpD1onK hRHd/Iu+aL3XRO8GQyaOT0x1vOm+XymyegEYvH8yd2gTTLX09HzEEU1qAcKS6q6pzqlByFuZDLNgv HLO1XdPe+eUfiwR9nyRcGXEB4T9DijBsBNiM/58uTlHJ7bumorb/Qdkb/z6MvAVMVcGN7OHM76a7B OnHvxJ2FUPeLIOZnnddel941I6HuGmYvov7c1upfFjQmI/bEl3HwSWbkUP3QFVD1mlGGTxQbH2PZd BbKpibfQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1lqsNc-0051HA-Rl; Wed, 09 Jun 2021 07:12:07 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 0A1A33002CA; Wed, 9 Jun 2021 09:12:04 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id C06AE201DE6EE; Wed, 9 Jun 2021 09:12:04 +0200 (CEST) Date: Wed, 9 Jun 2021 09:12:04 +0200 From: Peter Zijlstra To: Julia Lawall Cc: Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Mel Gorman , linux-kernel@vger.kernel.org Subject: Re: find_new_ilb Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 08, 2021 at 09:51:30PM +0200, Julia Lawall wrote: > Starting from the following commit: > > commit 45da7a2b0af8fa29dff2e6ba8926322068350fce > Author: Peter Zijlstra > Date: Tue Aug 18 10:48:17 2020 +0200 > > sched/fair: Exclude the current CPU from find_new_ilb() > > up through Linux 5.12, I observed that often when most of the machine was > idle, there could be many (thousands) of sched_wake_idle_without_ipi > events, typically between cores 0 and 1. I don't see this any more in > Linux v5.13-rc1. I looked through the patches to fair.c and core.c > subsequent to v5.12, and I didn't see anything that explicitly addresses > this issue. Before I plunge into another set of rounds of bisecting, I > wonder if anyone knows whether and how this problem was resolved? Hurmph.. that patch was preparation for a later change that never seems to have happened. If it is causing trouble for you, I think you can savely revert it. At the time I thought it was very strange that new_idle would select itself as idle-balancer, doubly so, because the only way to get there would be with NEED_RESCHED already set, so the IPI wouldn't in fact do anything. Looking again, the difference is ofcourse that previously we'd select self and NO-OP, but now we'll potentially select another CPU and actually do something. This is arguably an improvement, because we did want to do something. I can't quite remember what would've change here since, Vincent, can you remember? Anyway, is this actually causing you trouble, or are you just going on the increased number of events?