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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 3AA45C10DCE for ; Fri, 6 Mar 2020 16:00:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0AF212073D for ; Fri, 6 Mar 2020 16:00:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583510440; bh=nbAHA1WahxgO35nO+HhwXLm7RmPwbLsiDfTj5Z3wtuY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=zAAxhTOa8v3tT/P3Tz8XQyWNqNxjajAFCnYG5Qy5Wqd9iUZ9t8IbvONYKo32UrDUR f/88ZfKYPhl0IYZMbm9ZQR9TJZ9hgEMv4CIUmprBT/Iko8kVsYZJYYKLG+VSK1P5xl tAmGdVJuUAp+BYzQpDuirFpAqHM+esE5JtI74Rp4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726269AbgCFQAj (ORCPT ); Fri, 6 Mar 2020 11:00:39 -0500 Received: from mail.kernel.org ([198.145.29.99]:35056 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725935AbgCFQAj (ORCPT ); Fri, 6 Mar 2020 11:00:39 -0500 Received: from localhost (lfbn-ncy-1-985-231.w90-101.abo.wanadoo.fr [90.101.63.231]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 57FD62072A; Fri, 6 Mar 2020 16:00:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583510438; bh=nbAHA1WahxgO35nO+HhwXLm7RmPwbLsiDfTj5Z3wtuY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RXuEwq58XWL66xOdJk0nkgY5LaZFkURF9dB1PupzeUJDfjLHH0IyC5acMAA7SOLXk GP+iC/MrX8N0QCe3qoaviZNve1eGKSjkzLpNL5K1dB70vv0XeSxZfeVFVF8wNh9kSs 2rNH6zagvGemfUaQL+1vPezMgKk3H5vqR1j5QhkI= Date: Fri, 6 Mar 2020 17:00:36 +0100 From: Frederic Weisbecker To: Alex Belits Cc: "rostedt@goodmis.org" , "mingo@kernel.org" , "peterz@infradead.org" , "linux-kernel@vger.kernel.org" , Prasun Kapoor , "tglx@linutronix.de" , "linux-api@vger.kernel.org" , "linux-mm@vger.kernel.org" , "linux-arch@vger.kernel.org" Subject: Re: [PATCH 03/12] task_isolation: userspace hard isolation from kernel Message-ID: <20200306160035.GD8590@lenoir> References: <4473787e1b6bc3cc226067e8d122092a678b63de.camel@marvell.com> <36d84b8dd168a38e6a56549dedc15dd6ebf8c09e.camel@marvell.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <36d84b8dd168a38e6a56549dedc15dd6ebf8c09e.camel@marvell.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Wed, Mar 04, 2020 at 04:07:12PM +0000, Alex Belits wrote: > +#ifdef CONFIG_TASK_ISOLATION > +int try_stop_full_tick(void) > +{ > + int cpu = smp_processor_id(); > + struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); > + > + /* For an unstable clock, we should return a permanent error code. */ > + if (atomic_read(&tick_dep_mask) & TICK_DEP_MASK_CLOCK_UNSTABLE) > + return -EINVAL; > + > + if (!can_stop_full_tick(cpu, ts)) > + return -EAGAIN; Note that the stop_tick naming in nohz can be misleading. It means we actually leave the periodic mode and we enter in dynamic tick mode. In practice it means that the tick is delayed until the next event, which in the worst case may well be in 1 ms and in the best case never. So what you probably want to check instead is whether the tick has been entirely stopped (ie: we called hrtimer_cancel(&ts->sched_timer)). Thanks. > + > + tick_nohz_stop_sched_tick(ts, cpu); > + return 0; > +} > +#endif > + > static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) > { > /* > -- > 2.20.1 >