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=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, 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 5A9ABC433DB for ; Thu, 28 Jan 2021 20:26:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0F65364DA1 for ; Thu, 28 Jan 2021 20:26:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231483AbhA1U0M (ORCPT ); Thu, 28 Jan 2021 15:26:12 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:59991 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231154AbhA1UZ3 (ORCPT ); Thu, 28 Jan 2021 15:25:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611865442; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=09rgXsilTnae6yAI2+7X50tmB4yjigjLFKTbsUMux9E=; b=FP77sg8k1DJmCD6VkmYjyFY8o9s0GLqDiNtGmcch/pQIyCiM8J+EWZ5vP4Cw8N61mxsTvN uEOze99h09Zqnfw/k2U13STHD9sRN9dGg6gHUcvx9/GH8CrtfAUFGxTWKMiHODItn1WAlp ZQRMuDmQtI/fTNbeiCh1vlKPVseNXBg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-424-ERh-iRLwPrKqEYWt_23fTg-1; Thu, 28 Jan 2021 15:24:00 -0500 X-MC-Unique: ERh-iRLwPrKqEYWt_23fTg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 74B03107ACE3; Thu, 28 Jan 2021 20:23:59 +0000 (UTC) Received: from fuller.cnet (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1B1425D9EF; Thu, 28 Jan 2021 20:23:59 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id 122924178900; Thu, 28 Jan 2021 17:23:35 -0300 (-03) Message-ID: <20210128202235.818590134@fuller.cnet> User-Agent: quilt/0.66 Date: Thu, 28 Jan 2021 17:21:35 -0300 From: Marcelo Tosatti To: Peter Zijlstra , Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, Marcelo Tosatti Subject: [patch 1/3] nohz: only wakeup a single target cpu when kicking a task References: <20210128202134.608115362@fuller.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. From: Frederic Weisbecker Suggested-by: Peter Zijlstra Signed-off-by: Frederic Weisbecker Signed-off-by: Marcelo Tosatti Index: linux-2.6/kernel/time/tick-sched.c =================================================================== --- linux-2.6.orig/kernel/time/tick-sched.c +++ linux-2.6/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(); +} + /* * Kick all full dynticks CPUs in order to force these to re-evaluate * their dependency on the tick and restart it if necessary. @@ -404,19 +429,8 @@ EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cp */ void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit) { - if (!atomic_fetch_or(BIT(bit), &tsk->tick_dep_mask)) { - if (tsk == current) { - preempt_disable(); - tick_nohz_full_kick(); - preempt_enable(); - } else { - /* - * Some future tick_nohz_full_kick_task() - * should optimize this. - */ - tick_nohz_full_kick_all(); - } - } + if (!atomic_fetch_or(BIT(bit), &tsk->tick_dep_mask)) + tick_nohz_kick_task(tsk); } EXPORT_SYMBOL_GPL(tick_nohz_dep_set_task);