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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,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 9D718C433B4 for ; Wed, 5 May 2021 13:43:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6CA85613BA for ; Wed, 5 May 2021 13:43:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232923AbhEENol (ORCPT ); Wed, 5 May 2021 09:44:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55980 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232504AbhEENok (ORCPT ); Wed, 5 May 2021 09:44:40 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7677C061574 for ; Wed, 5 May 2021 06:43:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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; bh=ouVU1lFGYesDJ408JaUblRc5MBOEnLO2xbqaLV8Nsok=; b=iXS8hXw2F1CMw7wHZ0GTh7QZKn sr0rloRAgm/LZ/LVUSSF7qPmf4bwFVOmzL+b+qRzyEDrXGzAqvBEGc0N7QTCrcLKDAAyYeZUFEBYQ GsWsvZNNtHcghgnZn3vFH7r2+OxxakVeUmzxTA2oinojgyC4CJz/TLUv2RU67cdM0AGLEX0K93Lo0 EcYTfOtpteaYq7aiQXADap/HIuVEjcYFYNUeCaN7w0dJsbtTj9QZGSl+1m+3gHG3yX05xB4WIaGyX GYON0eaiOAMcT1pKZzSl2896FotWSMvJ/Hlf0nVTG9UwJPOrBlYKll8jyEUYyDVT4Qvr+dxkY0+i9 d0jG7RRw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1leHoI-001KjC-P4; Wed, 05 May 2021 13:43:31 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4EEF63001CD; Wed, 5 May 2021 15:43:29 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id EF9F12027AFE6; Wed, 5 May 2021 15:43:28 +0200 (CEST) Date: Wed, 5 May 2021 15:43:28 +0200 From: Peter Zijlstra To: Frederic Weisbecker Cc: Thomas Gleixner , LKML , "Rafael J . Wysocki" , Yunfeng Ye , Marcelo Tosatti Subject: Re: [PATCH 6/8] tick/nohz: Only wakeup a single target cpu when kicking a task Message-ID: References: <20210422120158.33629-1-frederic@kernel.org> <20210422120158.33629-7-frederic@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210422120158.33629-7-frederic@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 22, 2021 at 02:01:56PM +0200, Frederic Weisbecker wrote: > When adding a tick dependency to a task, its necessary to > wakeup the CPU where the task resides to reevaluate tick > dependencies on that CPU. > > However the current code wakes up all nohz_full CPUs, which > is unnecessary. > > Switch to waking up a single CPU, by using ordering of writes > to task->cpu and task->tick_dep_mask. > > Suggested-by: Peter Zijlstra > Signed-off-by: Frederic Weisbecker > Cc: Yunfeng Ye > Cc: Thomas Gleixner > Cc: Rafael J. Wysocki > Signed-off-by: Marcelo Tosatti > --- > kernel/time/tick-sched.c | 40 +++++++++++++++++++++++++++------------- > 1 file changed, 27 insertions(+), 13 deletions(-) > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index ffc13b9dfbe3..45d9a4ea3ee0 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -322,6 +322,31 @@ void tick_nohz_full_kick_cpu(int cpu) > irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu); > } > > +static void tick_nohz_kick_task(struct task_struct *tsk) > +{ > + int cpu = task_cpu(tsk); > + > + /* > + * If the task concurrently migrates to another cpu, > + * we guarantee it sees the new tick dependency upon > + * schedule. > + * > + * > + * set_task_cpu(p, cpu); > + * STORE p->cpu = @cpu > + * __schedule() (switch to task 'p') > + * LOCK rq->lock > + * smp_mb__after_spin_lock() STORE p->tick_dep_mask > + * tick_nohz_task_switch() smp_mb() (atomic_fetch_or()) > + * LOAD p->tick_dep_mask LOAD p->cpu > + */ > + > + preempt_disable(); > + if (cpu_online(cpu)) > + tick_nohz_full_kick_cpu(cpu); > + preempt_enable(); > +} That had me looking at tick_nohz_task_switch(), does we want the below? diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 9143163fa678..ff45fc513ba7 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4207,6 +4207,7 @@ static struct rq *finish_task_switch(struct task_struct *prev) vtime_task_switch(prev); perf_event_task_sched_in(prev, current); finish_task(prev); + tick_nohz_task_switch(); finish_lock_switch(rq); finish_arch_post_lock_switch(); kcov_finish_switch(current); @@ -4252,7 +4253,6 @@ static struct rq *finish_task_switch(struct task_struct *prev) put_task_struct_rcu_user(prev); } - tick_nohz_task_switch(); return rq; } diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 828b091501ca..ea079be9097f 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -447,13 +447,10 @@ void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bi */ void __tick_nohz_task_switch(void) { - unsigned long flags; struct tick_sched *ts; - local_irq_save(flags); - if (!tick_nohz_full_cpu(smp_processor_id())) - goto out; + return; ts = this_cpu_ptr(&tick_cpu_sched); @@ -462,8 +459,6 @@ void __tick_nohz_task_switch(void) atomic_read(¤t->signal->tick_dep_mask)) tick_nohz_full_kick(); } -out: - local_irq_restore(flags); } /* Get the boot-time nohz CPU list from the kernel parameters. */