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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 4F6B4C00449 for ; Fri, 5 Oct 2018 14:27:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 209C5213A2 for ; Fri, 5 Oct 2018 14:27:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 209C5213A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.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 S1728890AbeJEVZ6 (ORCPT ); Fri, 5 Oct 2018 17:25:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:52240 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727968AbeJEVZ5 (ORCPT ); Fri, 5 Oct 2018 17:25:57 -0400 Received: from gandalf.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 67B462087D; Fri, 5 Oct 2018 14:27:00 +0000 (UTC) Date: Fri, 5 Oct 2018 10:26:58 -0400 From: Steven Rostedt To: Peng Hao Cc: mingo@redhat.com, peterz@infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] sched/rt : return accurate release rq lock info Message-ID: <20181005102658.38ecde83@gandalf.local.home> In-Reply-To: <1538778131-44406-1-git-send-email-peng.hao2@zte.com.cn> References: <1538778131-44406-1-git-send-email-peng.hao2@zte.com.cn> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 6 Oct 2018 06:22:11 +0800 Peng Hao wrote: > find_lock_lowest_rq may or not releease rq lock when return > lowest_rq=NULL, but it is fuzzy. > If not releasing rq lock, it is unnecessary to re-call > pick_next_pushable_task. > When CONFIG_PREEMPT=n, not releasing rq lock and return > lowest_rq=null frequently happens in a simple test case: > Four different rt priority tasks run on limited two cpus. > Thanks for Steven Rostedt's advice. > > Signed-off-by: Peng Hao > --- > kernel/sched/rt.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index 2e2955a..be0fc43 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1754,7 +1754,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) > !task_on_rq_queued(task))) { > > double_unlock_balance(rq, lowest_rq); > - lowest_rq = NULL; > + lowest_rq = RETRY_TASK; > break; > } > } > @@ -1830,7 +1830,9 @@ static int push_rt_task(struct rq *rq) > > /* find_lock_lowest_rq locks the rq if found */ > lowest_rq = find_lock_lowest_rq(next_task, rq); > - if (!lowest_rq) { > + if (!lowest_rq) > + goto out; > + if (lowest_rq == RETRY_TASK) { This probably makes no difference, and can be blown off as just a preference, but should this be: if (!lowest_rq) { goto out; } else if (lowest_rq == RETRY_TASK) { The logic is the same regardless, so it's really just a matter of taste. That said: Reviewed-by: Steven Rostedt (VMware) -- Steve > struct task_struct *task; > /* > * find_lock_lowest_rq releases rq->lock