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=-3.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 3E348C4363A for ; Thu, 8 Oct 2020 14:59:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9DFD82076E for ; Thu, 8 Oct 2020 14:59:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Yv0zXgOv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730784AbgJHO7q (ORCPT ); Thu, 8 Oct 2020 10:59:46 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:56236 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730749AbgJHO7q (ORCPT ); Thu, 8 Oct 2020 10:59:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1602169184; 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: in-reply-to:in-reply-to:references:references; bh=e06xMkbB2fD5VIcvUFWfr+X35EMRsZKUGRjfiwycl3I=; b=Yv0zXgOvfjC6z2P0fDdJZoxF4PZ62wih6L7WsDygG5mbKxOdTJcIL7RLJeqdLkaVTd1a4C IPEizHOUze726J/eVM4r8RGt9dTzMG3zRRvuJAMkl/efK1FlYuzFWIIQ+VpAo1ElgO9WtW KKvu7Jh6/E+OrPb3xrlObsXeQ9aEgA4= Received: from mail-qk1-f197.google.com (mail-qk1-f197.google.com [209.85.222.197]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-530-CJSDYk4eNTivQ4o_TCBI5A-1; Thu, 08 Oct 2020 10:59:43 -0400 X-MC-Unique: CJSDYk4eNTivQ4o_TCBI5A-1 Received: by mail-qk1-f197.google.com with SMTP id f126so4110916qke.17 for ; Thu, 08 Oct 2020 07:59:43 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=e06xMkbB2fD5VIcvUFWfr+X35EMRsZKUGRjfiwycl3I=; b=PqouK4PkUEQ5QN9gfEp5MlXq/NakI/fN549Gpvv/mdyxPoXPSW3hvny5T+OrKNV5YW tltDoV0Xquu1WB47WeLE7f1NKPzAsyMLw/OXwcVW6uxDEVTeO3Ss5C6Fspf2AcnwYvuy ipEKQbayD5LhAb549rqFFRh1kBKovJSywFCiZAYYTn/0MmCOCHEAfmTGsKuJIECPpsEF HePczVQ8SbT0wn6WNsPx0P5hu4p9W0aJ9Ix+t5j+Z5tsfM9TlTvmYOQD84JC9DzYHDpa 5iNmkP1mXPU0OqCVrz04GVY9qnAwhEjYaUTqKfZArwQhB3+X+/pfo5a6ckieSQAOGHVX ztxQ== X-Gm-Message-State: AOAM530RFDxpJ48lJUD6qNQDJ0kl9fMW17ArcQkWIbEhmzTsptPcCuNI P7T+aa9FwN4Xdfvr8o+7Wr7QL2OHrmV2/94VutBLbDXnsVhdbqEx3alsO8XaiNxGEpF+ofpdCKA lqgRYMoPlZ0Z3Ft6GBL517tbE X-Received: by 2002:a05:620a:13c4:: with SMTP id g4mr1861457qkl.400.1602169182555; Thu, 08 Oct 2020 07:59:42 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwIMNe5KE1NedAJX8Du5b1Ll7xdHO6GNVZI1BSKymJg0vDH3s0WT0Q4YdPvX8KSH3zI1BmlYg== X-Received: by 2002:a05:620a:13c4:: with SMTP id g4mr1861435qkl.400.1602169182309; Thu, 08 Oct 2020 07:59:42 -0700 (PDT) Received: from xz-x1 (toroon474qw-lp140-04-174-95-215-133.dsl.bell.ca. [174.95.215.133]) by smtp.gmail.com with ESMTPSA id q9sm4174423qta.70.2020.10.08.07.59.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Oct 2020 07:59:41 -0700 (PDT) Date: Thu, 8 Oct 2020 10:59:40 -0400 From: Peter Xu To: Marcelo Tosatti Cc: linux-kernel@vger.kernel.org, Frederic Weisbecker , Peter Zijlstra , Nitesh Narayan Lal Subject: Re: [patch 1/2] nohz: only wakeup a single target cpu when kicking a task Message-ID: <20201008145940.GG6026@xz-x1> References: <20201007180151.623061463@redhat.com> <20201007180229.724302019@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201007180229.724302019@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 07, 2020 at 03:01:52PM -0300, Marcelo Tosatti wrote: > +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(); Pure question: is preempt_disable() required here? Same question to tick_nohz_full_kick_all(). > + if (cpu_online(cpu)) > + tick_nohz_full_kick_cpu(cpu); > + preempt_enable(); > +} -- Peter Xu