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 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 BDDEBC004D2 for ; Tue, 2 Oct 2018 15:18:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 679882089A for ; Tue, 2 Oct 2018 15:18:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 679882089A 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 S1726756AbeJBWCM (ORCPT ); Tue, 2 Oct 2018 18:02:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:35510 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726533AbeJBWCM (ORCPT ); Tue, 2 Oct 2018 18:02:12 -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 16167206B2; Tue, 2 Oct 2018 15:18:18 +0000 (UTC) Date: Tue, 2 Oct 2018 11:18:16 -0400 From: Steven Rostedt To: Peng Hao Cc: mingo@redhat.com, peterz@infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] sched/rt : return accurate release rq lock info Message-ID: <20181002111816.0d752a4b@gandalf.local.home> In-Reply-To: <1538511442-20182-1-git-send-email-peng.hao2@zte.com.cn> References: <1538511442-20182-1-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 Wed, 3 Oct 2018 04:17:22 +0800 Peng Hao wrote: > find_lock_lowest_rq may or not releease rq lock, 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 frequently happens > in a simple test case: > Four different rt priority tasks run on limited two cpus. > > Signed-off-by: Peng Hao > --- > kernel/sched/rt.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index 2e2955a..7c5382a 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1718,6 +1718,7 @@ static int find_lowest_rq(struct task_struct *task) > static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) > { > struct rq *lowest_rq = NULL; > + bool release_lock = false; > int tries; > int cpu; > > @@ -1741,6 +1742,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) > > /* if the prio of this runqueue changed, try again */ > if (double_lock_balance(rq, lowest_rq)) { > + release_lock = true; > /* > * We had to unlock the run queue. In > * the mean time, task could have > @@ -1768,6 +1770,8 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) > lowest_rq = NULL; > } > > + if (!lowest_rq && release_lock) > + lowest_rq = RETRY_TASK; > return lowest_rq; > } Instead of adding the above boolean variable, wouldn't this work just as well? diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 2e2955a8cf8f..b363ef70412a 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 +1834,7 @@ 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) { Not a biggy, but I would add here: if (!lowest_rq) goto out; And then add the below. It just flows better. -- Steve > + if (lowest_rq == RETRY_TASK) { > struct task_struct *task; > /* > * find_lock_lowest_rq releases rq->lock > @@ -1863,6 +1867,8 @@ static int push_rt_task(struct rq *rq) > goto retry; > } > > + if (!lowest_rq) > + goto out; > deactivate_task(rq, next_task, 0); > set_task_cpu(next_task, lowest_rq->cpu); > activate_task(lowest_rq, next_task, 0);