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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,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 E6331C43387 for ; Wed, 9 Jan 2019 18:24:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B60E3214C6 for ; Wed, 9 Jan 2019 18:24:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727004AbfAISYV (ORCPT ); Wed, 9 Jan 2019 13:24:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:35910 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726869AbfAISYU (ORCPT ); Wed, 9 Jan 2019 13:24:20 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B8010356CF; Wed, 9 Jan 2019 18:24:20 +0000 (UTC) Received: from sky.random (ovpn-123-111.rdu2.redhat.com [10.10.123.111]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5EE9710A1839; Wed, 9 Jan 2019 18:24:20 +0000 (UTC) Date: Wed, 9 Jan 2019 13:24:18 -0500 From: Andrea Arcangeli To: Mel Gorman Cc: Mike Galbraith , Peter Zijlstra , linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/1] RFC: sched/fair: skip select_idle_sibling() in presence of sync wakeups Message-ID: <20190109182418.GB28624@redhat.com> References: <20190109034941.28759-1-aarcange@redhat.com> <1547007588.17100.17.camel@gmx.de> <20190109100751.GQ31517@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190109100751.GQ31517@techsingularity.net> User-Agent: Mutt/1.11.1 (2018-12-01) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 09 Jan 2019 18:24:20 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 09, 2019 at 10:07:51AM +0000, Mel Gorman wrote: > I agree with Mike here. Many previous attempts to strictly obey the strict > hint has led to regressions elsewhere -- specifically a task waking 2+ > wakees that temporarily stack on one CPU when nearby CPUs sharing LLC sync-waking 2 wakees in a row before going to sleep should cause the runqueue to have nr_running != 1 after the first wakee is waken up on the local CPU. Your example explains the following nr_running == 1 check in the patch: (sync && target == this_cpu && cpu_rq(this_cpu)->nr_running == 1)) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The implementation is just an RFC because it may have other drawbacks, but I thought the second wakee of this specific example supposedly should still do the idle core/ht balancing normally like before the change. Thanks, Andrea