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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,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 C2224C04EBD for ; Tue, 16 Oct 2018 12:35:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 73D1E20866 for ; Tue, 16 Oct 2018 12:35:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="U2reL9tp" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 73D1E20866 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.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 S1727105AbeJPUZk (ORCPT ); Tue, 16 Oct 2018 16:25:40 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:49990 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726778AbeJPUZk (ORCPT ); Tue, 16 Oct 2018 16:25:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; 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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=MIFkZXafsgU0n0h5B1FEhA7PnV97YNSnHnNN/NRLA0Y=; b=U2reL9tp38KrZYiR4ZWersSpN /lkWBEP8hgUU4apBFDAHg7FI9cndFkDUnVYwGHsMN5KzMXkWZ7stMSPE+IhzOei3Yj4f5xh2Czr9F pYhcJWCJ3R129ukWc1COgKcYVF/hqrR+Do/lPAyrDwFmJXiVMOpEplV8+wqNEPPkZxi4+qg0/FiSx pJ3ksT1nLgegouK2PrnsJwYIGIEx6V6169BIOoFIRK7IOr32xHx1DnKuEaYZQnDSmmRvUQ3X0WEWi lHk1tSiiqI9pnr1Uc0ETtAFIXQW6Tn+gnbSeRuLibSjPugHK1YFXpCu4EpkUj5FL3PetcVbjiuZ1H a/jOhzHbw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gCOZE-00032K-Mu; Tue, 16 Oct 2018 12:35:21 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 409E620297B7B; Tue, 16 Oct 2018 14:35:17 +0200 (CEST) Date: Tue, 16 Oct 2018 14:35:17 +0200 From: Peter Zijlstra To: Steven Rostedt Cc: Peng Hao , mingo@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] sched/rt : return accurate release rq lock info Message-ID: <20181016123517.GB2537@hirez.programming.kicks-ass.net> References: <1538778131-44406-1-git-send-email-peng.hao2@zte.com.cn> <20181015092032.GO9867@hirez.programming.kicks-ass.net> <20181015114220.70c3598d@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181015114220.70c3598d@gandalf.local.home> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 15, 2018 at 11:42:20AM -0400, Steven Rostedt wrote: > On Mon, 15 Oct 2018 11:20:32 +0200 > Peter Zijlstra wrote: > > > > 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; > > > } > > > } > > > > I'm confused.. should not: > > > > /* try again */ > > double_unlock_balance(rq, lowest_rq); > > lowest_rq = NULL; > > > > also return RETRY_TASK? That also is in the double_lock_balance() path > > and will this have had rq->lock() released. > > I thought the same thing at first, but this is in the loop path, where > it does everything again. But now looking closer, I think there's a bug > in the original code. So I find that whole thing utterly confusing; what about we start with something like so? --- kernel/sched/rt.c | 51 +++++++++++++++++++++++---------------------------- 1 file changed, 23 insertions(+), 28 deletions(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 2e2955a8cf8f..237c84c2b042 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1714,6 +1714,26 @@ static int find_lowest_rq(struct task_struct *task) return -1; } +static struct task_struct *first_pushable_task(struct rq *rq) +{ + struct task_struct *p; + + if (!has_pushable_tasks(rq)) + return NULL; + + p = plist_first_entry(&rq->rt.pushable_tasks, + struct task_struct, pushable_tasks); + + BUG_ON(rq->cpu != task_cpu(p)); + BUG_ON(task_current(rq, p)); + BUG_ON(p->nr_cpus_allowed <= 1); + + BUG_ON(!task_on_rq_queued(p)); + BUG_ON(!rt_task(p)); + + return p; +} + /* Will lock the rq it finds */ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) { @@ -1747,12 +1767,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) * migrated already or had its affinity changed. * Also make sure that it wasn't scheduled on its rq. */ - if (unlikely(task_rq(task) != rq || - !cpumask_test_cpu(lowest_rq->cpu, &task->cpus_allowed) || - task_running(rq, task) || - !rt_task(task) || - !task_on_rq_queued(task))) { - + if (first_pushable_task(rq) != task) double_unlock_balance(rq, lowest_rq); lowest_rq = NULL; break; @@ -1771,26 +1786,6 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) return lowest_rq; } -static struct task_struct *pick_next_pushable_task(struct rq *rq) -{ - struct task_struct *p; - - if (!has_pushable_tasks(rq)) - return NULL; - - p = plist_first_entry(&rq->rt.pushable_tasks, - struct task_struct, pushable_tasks); - - BUG_ON(rq->cpu != task_cpu(p)); - BUG_ON(task_current(rq, p)); - BUG_ON(p->nr_cpus_allowed <= 1); - - BUG_ON(!task_on_rq_queued(p)); - BUG_ON(!rt_task(p)); - - return p; -} - /* * If the current CPU has more than one RT task, see if the non * running task can migrate over to a CPU that is running a task @@ -1805,7 +1800,7 @@ static int push_rt_task(struct rq *rq) if (!rq->rt.overloaded) return 0; - next_task = pick_next_pushable_task(rq); + next_task = first_pushable_task(rq); if (!next_task) return 0; @@ -1840,7 +1835,7 @@ static int push_rt_task(struct rq *rq) * run-queue and is also still the next task eligible for * pushing. */ - task = pick_next_pushable_task(rq); + task = first_pushable_task(rq); if (task == next_task) { /* * The task hasn't migrated, and is still the next