From: Frederic Weisbecker <fweisbec@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Rik van Riel <riel@redhat.com>,
James Hartsock <hartsjc@redhat.com>,
stable@vger.kernel.org, Tim Wright <tim@binbash.co.uk>,
Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH 2/2] tick: Make sure tick timer is active when bypassing reprogramming
Date: Fri, 21 Apr 2017 01:27:47 +0200 [thread overview]
Message-ID: <20170420232746.GF25160@lerouge> (raw)
In-Reply-To: <alpine.DEB.2.20.1704202137440.2373@nanos>
On Thu, Apr 20, 2017 at 09:40:12PM +0200, Thomas Gleixner wrote:
> On Thu, 20 Apr 2017, Frederic Weisbecker wrote:
> > On Thu, Apr 20, 2017 at 07:56:22PM +0200, Thomas Gleixner wrote:
> > > > /* Skip reprogram of event if its not changed */
> > > > - if (ts->tick_stopped && (expires == ts->next_tick))
> > > > + if (ts->tick_stopped && (expires == ts->next_tick)) {
> > > > + WARN_ON_ONCE(dev->next_event > ts->next_tick);
> > >
> > > What about handling it proper ? dev->next_event might be KTIME_MAX,
> > > i.e. no more event for the next 500+ years.
> >
> > I thought I handled this case, what I'm I missing?
>
> if (ts->tick_stopped && (expires == ts->next_tick)) {
> WARN_ON_ONCE(dev->next_event > ts->next_tick);
> goto out;
> }
>
> IOW, the WARN_ON yells in dmesg, but despite seing the wreckage it just
> leaves it and goes out doing nothing.
>
> Why can't you just do
>
> if (ts->tick_stopped && (expires == ts->next_tick)) {
> if (dev->next_event > ts->next_tick)) {
> WARN_ONCE();
> do_something_sensible();
> }
> goto out;
> }
>
> Hmm?
Ah ok, right!
So something like this:
if (ts->tick_stopped && (expires == ts->next_tick)) {
if (likely(dev->next_event <= ts->next_tick))
goto out;
WARN_ON_ONCE(1);
}
So that we fall down to clock reprogramming if the sanity check fails.
I'm resending the patches.
Thanks.
next prev parent reply other threads:[~2017-04-20 23:27 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-20 15:30 [PATCH 0/2] nohz: Deal with clock reprogram skipping issues Frederic Weisbecker
2017-04-20 15:30 ` [PATCH 1/2] nohz: Fix again collision between tick and other hrtimers Frederic Weisbecker
2017-04-20 16:00 ` Rik van Riel
2017-04-20 15:30 ` [PATCH 2/2] tick: Make sure tick timer is active when bypassing reprogramming Frederic Weisbecker
2017-04-20 16:01 ` Rik van Riel
2017-04-20 17:56 ` Thomas Gleixner
2017-04-20 18:29 ` Frederic Weisbecker
2017-04-20 19:40 ` Thomas Gleixner
2017-04-20 23:27 ` Frederic Weisbecker [this message]
2017-04-21 14:00 [PATCH 0/2] nohz: Deal with clock reprogram skipping issues v2 Frederic Weisbecker
2017-04-21 14:00 ` [PATCH 2/2] tick: Make sure tick timer is active when bypassing reprogramming Frederic Weisbecker
2017-06-03 8:06 ` Levin, Alexander (Sasha Levin)
2017-06-03 12:42 ` Frederic Weisbecker
2017-06-03 13:00 ` Levin, Alexander (Sasha Levin)
2017-06-06 14:52 ` Frederic Weisbecker
2017-06-07 4:17 ` Levin, Alexander (Sasha Levin)
2017-06-07 14:14 ` Frederic Weisbecker
2017-06-07 21:36 ` Levin, Alexander (Sasha Levin)
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