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=-8.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 4A911CA90AF for ; Wed, 13 May 2020 12:45:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 21C0A20659 for ; Wed, 13 May 2020 12:45:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hSEbV3Gc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731920AbgEMMpv (ORCPT ); Wed, 13 May 2020 08:45:51 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:31866 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728379AbgEMMpv (ORCPT ); Wed, 13 May 2020 08:45:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589373949; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=FjjfCoKK48jzgXm67hbDCH1DJsihwHwCzqUHDeAkssg=; b=hSEbV3Gc012nJgv3eMzXzt7m4smiiH9vOC581qbKLt/GNagQx0rYme8ch5MMkXwSWymCW/ xB4/z8q5yhqoQi/dGXjFeTyXo1hoxDni+gMB2M2UKJ3rf3tqf2Yf2KNup5l6K3Q9gKuh6W MAf1aZuzsHAyh/v6Xca/fEmPLLBk2QQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-25-AZdOkNvpPAix6SYjViarcA-1; Wed, 13 May 2020 08:45:47 -0400 X-MC-Unique: AZdOkNvpPAix6SYjViarcA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 37F86107ACCD; Wed, 13 May 2020 12:45:46 +0000 (UTC) Received: from lorien.usersys.redhat.com (ovpn-113-165.phx2.redhat.com [10.3.113.165]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6B6DB62B1E; Wed, 13 May 2020 12:45:42 +0000 (UTC) Date: Wed, 13 May 2020 08:45:40 -0400 From: Phil Auld To: Vincent Guittot Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, linux-kernel@vger.kernel.org, ouwen210@hotmail.com, pkondeti@codeaurora.org Subject: Re: [PATCH v2] sched/fair: enqueue_task_fair optimization Message-ID: <20200513124540.GB12425@lorien.usersys.redhat.com> References: <20200513123335.28122-1-vincent.guittot@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200513123335.28122-1-vincent.guittot@linaro.org> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Vincent, On Wed, May 13, 2020 at 02:33:35PM +0200 Vincent Guittot wrote: > enqueue_task_fair jumps to enqueue_throttle label when cfs_rq_of(se) is > throttled which means that se can't be NULL and we can skip the test. > s/be NULL/be non-NULL/ I think. It's more like if it doesn't jump to the label then se must be NULL for the loop to terminate. The final loop is a NOP if se is NULL. The check wasn't protecting that. Otherwise still > Reviewed-by: Phil Auld Cheers, Phil > Signed-off-by: Vincent Guittot > --- > > v2 changes: > - Remove useless if statement > > kernel/sched/fair.c | 39 ++++++++++++++++++++------------------- > 1 file changed, 20 insertions(+), 19 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index a0c690d57430..b51b12d63c39 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5513,28 +5513,29 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) > list_add_leaf_cfs_rq(cfs_rq); > } > > -enqueue_throttle: > - if (!se) { > - add_nr_running(rq, 1); > - /* > - * Since new tasks are assigned an initial util_avg equal to > - * half of the spare capacity of their CPU, tiny tasks have the > - * ability to cross the overutilized threshold, which will > - * result in the load balancer ruining all the task placement > - * done by EAS. As a way to mitigate that effect, do not account > - * for the first enqueue operation of new tasks during the > - * overutilized flag detection. > - * > - * A better way of solving this problem would be to wait for > - * the PELT signals of tasks to converge before taking them > - * into account, but that is not straightforward to implement, > - * and the following generally works well enough in practice. > - */ > - if (flags & ENQUEUE_WAKEUP) > - update_overutilized_status(rq); > + /* At this point se is NULL and we are at root level*/ > + add_nr_running(rq, 1); > + > + /* > + * Since new tasks are assigned an initial util_avg equal to > + * half of the spare capacity of their CPU, tiny tasks have the > + * ability to cross the overutilized threshold, which will > + * result in the load balancer ruining all the task placement > + * done by EAS. As a way to mitigate that effect, do not account > + * for the first enqueue operation of new tasks during the > + * overutilized flag detection. > + * > + * A better way of solving this problem would be to wait for > + * the PELT signals of tasks to converge before taking them > + * into account, but that is not straightforward to implement, > + * and the following generally works well enough in practice. > + */ > + if (flags & ENQUEUE_WAKEUP) > + update_overutilized_status(rq); > > } > > +enqueue_throttle: > if (cfs_bandwidth_used()) { > /* > * When bandwidth control is enabled; the cfs_rq_throttled() > -- > 2.17.1 > --