From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752806AbeCPOQs (ORCPT <rfc822;w@1wt.eu>);
        Fri, 16 Mar 2018 10:16:48 -0400
Received: from mail.kernel.org ([198.145.29.99]:45150 "EHLO mail.kernel.org"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1752683AbeCPOQj (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 16 Mar 2018 10:16:39 -0400
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C0A7E217CE
Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org
Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=frederic@kernel.org
Date: Fri, 16 Mar 2018 15:16:35 +0100
From: Frederic Weisbecker <frederic@kernel.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Thomas Ilsche <thomas.ilsche@tu-dresden.de>,
        Doug Smythies <dsmythies@telus.net>, Rik van Riel <riel@surriel.com>,
        Aubrey Li <aubrey.li@linux.intel.com>,
        Mike Galbraith <mgalbraith@suse.de>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFT][PATCH v4 3/7] sched: idle: Do not stop the tick before
 cpuidle_idle_call()
Message-ID: <20180316141633.GA20981@lerouge>
References: <2352117.3UUoYAu18A@aspire.rjw.lan>
 <3550231.xNMJN5JcLx@aspire.rjw.lan>
 <20180315181858.GA14983@lerouge>
 <CAJZ5v0jGi_ewnJXxwuY1-y6Ti64Y601A4DQuDhtMJ+riYPJpzA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAJZ5v0jGi_ewnJXxwuY1-y6Ti64Y601A4DQuDhtMJ+riYPJpzA@mail.gmail.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Mar 15, 2018 at 09:41:10PM +0100, Rafael J. Wysocki wrote:
> On Thu, Mar 15, 2018 at 7:19 PM, Frederic Weisbecker
> <frederic@kernel.org> wrote:
> > On Mon, Mar 12, 2018 at 10:53:25AM +0100, Rafael J. Wysocki wrote:
> >> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >>
> >> Make cpuidle_idle_call() decide whether or not to stop the tick.
> >>
> >> First, the cpuidle_enter_s2idle() path deals with the tick (and with
> >> the entire timekeeping for that matter) by itself and it doesn't need
> >> the tick to be stopped beforehand.
> >
> > Not sure you meant timekeeping either :)
> 
> Yeah, I meant nohz.
> 
> >>       if (idle_should_enter_s2idle() || dev->use_deepest_state) {
> >>               if (idle_should_enter_s2idle()) {
> >> +                     rcu_idle_enter();
> >> +
> >>                       entered_state = cpuidle_enter_s2idle(drv, dev);
> >>                       if (entered_state > 0) {
> >>                               local_irq_enable();
> >>                               goto exit_idle;
> >>                       }
> >> +
> >> +                     rcu_idle_exit();
> >>               }
> >
> > I'm not sure how the tick is stopped on suspend to idle. Perhaps through
> > hrtimer (tick_cancel_sched_timer()) or clockevents code.
> 
> The latter.
> 
> It does clockevents_shutdown() down the road, eventually.

Ah good. And I see tick_resume_oneshot() takes care of restoring if necessary.

> 
> IOW, it couldn't care less. :-)
> 
> > But we may have a similar problem than with idle_poll() called right after
> > call_cpuidle(). Ie: we arrive in cpuidle_enter_s2idle() with a tick that
> > should be reprogrammed while it is not. No idea if that can hurt somehow.
> >
> > I guess it depends what happens to the tick on s2idle, I'm not clear with that.
> 
> No problem there, AFAICS.

Yep, all good.

Thanks!