Re: [PATCH 2/2] tick: Make sure tick timer is active when bypassing reprogramming

From: Frederic Weisbecker <fweisbec@gmail.com>
To: "Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	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" <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: Sat, 3 Jun 2017 14:42:43 +0200	[thread overview]
Message-ID: <20170603124237.GA25077@lerouge> (raw)
In-Reply-To: <20170603080638.7okm4ztp7zuphc4b@sasha-lappy>

On Sat, Jun 03, 2017 at 08:06:41AM +0000, Levin, Alexander (Sasha Levin) wrote:
> On Fri, Apr 21, 2017 at 04:00:55PM +0200, Frederic Weisbecker wrote:
> > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> > index 502b320..be7ca4d 100644
> > --- a/kernel/time/tick-sched.c
> > +++ b/kernel/time/tick-sched.c
> > @@ -783,8 +783,13 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
> >  	tick = expires;
> >  
> >  	/* Skip reprogram of event if its not changed */
> > -	if (ts->tick_stopped && (expires == ts->next_tick))
> > -		goto out;
> > +	if (ts->tick_stopped && (expires == ts->next_tick)) {
> > +		/* Sanity check: make sure clockevent is actually programmed */
> > +		if (likely(dev->next_event <= ts->next_tick))
> > +			goto out;
> > +
> > +		WARN_ON_ONCE(1);
> > +	}
> 
> I seem to be hitting that in a KVM vm, even without load (sometimes
> right after boot):

Ah, can you tell me which tree you were using? Is it tip/master?
Can you give me its HEAD and your config file?

Thanks