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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 C45BCC433E9 for ; Wed, 13 Jan 2021 18:32:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 899A9233FC for ; Wed, 13 Jan 2021 18:32:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728408AbhAMScg (ORCPT ); Wed, 13 Jan 2021 13:32:36 -0500 Received: from foss.arm.com ([217.140.110.172]:40390 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728227AbhAMScf (ORCPT ); Wed, 13 Jan 2021 13:32:35 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9D2A81FB; Wed, 13 Jan 2021 10:31:49 -0800 (PST) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id EECBB3F66E; Wed, 13 Jan 2021 10:31:47 -0800 (PST) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: paulmck@kernel.org, peterz@infradead.org, mingo@kernel.org, tglx@linutronix.de, jiangshanlai@gmail.com, cai@redhat.com, vincent.donnefort@arm.com, decui@microsoft.com, vincent.guittot@linaro.org, rostedt@goodmis.org, tj@kernel.org Subject: [PATCH] sched/core: Print out straggler tasks in sched_cpu_dying() Date: Wed, 13 Jan 2021 18:31:41 +0000 Message-Id: <20210113183141.11974-1-valentin.schneider@arm.com> X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Since commit 1cf12e08bc4d ("sched/hotplug: Consolidate task migration on CPU unplug") tasks are expected to move themselves out of a out-going CPU. For most tasks this will be done automagically via BALANCE_PUSH, but percpu kthreads will have to cooperate and move themselves away one way or another. Currently, some percpu kthreads (workqueues being a notable exemple) do not cooperate nicely and can end up on an out-going CPU at the time sched_cpu_dying() is invoked. Print the dying rq's tasks to shed some light on the stragglers. Signed-off-by: Valentin Schneider --- As Peter pointed out, this should really be caught much earlier than sched_cpu_dying(). If we go down the route of preventing kthreads from being affined to !active CPUs in __set_cpus_allowed_ptr() (genuine percpu kthreads sidestep it via kthread_bind_mask()), then I *think* we could catch this in wakeups, i.e. select_task_rq(). I've been playing around there, but it's not as straightforward as I'd have hoped. --- kernel/sched/core.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 9a08a39d7cdb..d784dd1ae436 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7564,6 +7564,25 @@ static void calc_load_migrate(struct rq *rq) atomic_long_add(delta, &calc_load_tasks); } +static void dump_rq_tasks(struct rq *rq, const char *loglvl) +{ + struct task_struct *g, *p; + int cpu = cpu_of(rq); + + lockdep_assert_held(&rq->lock); + + printk("%sCPU%d enqueued tasks (%u total):\n", loglvl, cpu, rq->nr_running); + for_each_process_thread(g, p) { + if (task_cpu(p) != cpu) + continue; + + if (!task_on_rq_queued(p)) + continue; + + printk("%s\tpid: %d, name: %s\n", loglvl, p->pid, p->comm); + } +} + int sched_cpu_dying(unsigned int cpu) { struct rq *rq = cpu_rq(cpu); @@ -7573,7 +7592,10 @@ int sched_cpu_dying(unsigned int cpu) sched_tick_stop(cpu); rq_lock_irqsave(rq, &rf); - BUG_ON(rq->nr_running != 1 || rq_has_pinned_tasks(rq)); + if (rq->nr_running != 1 || rq_has_pinned_tasks(rq)) { + WARN(true, "Dying CPU not properly vacated!"); + dump_rq_tasks(rq, KERN_WARNING); + } rq_unlock_irqrestore(rq, &rf); calc_load_migrate(rq); -- 2.27.0