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

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Message-ID: <20170603125259.scyapxq2fftqiiz3@sasha-lappy>
Date:   Sat, 3 Jun 2017 13:00:53 +0000
From:   "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
To:     Frederic Weisbecker <fweisbec@...il.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rik van Riel" <riel@...hat.com>,
        James Hartsock <hartsjc@...hat.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Tim Wright <tim@...bash.co.uk>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 2/2] tick: Make sure tick timer is active when bypassing
 reprogramming

On Sat, Jun 03, 2017 at 02:42:43PM +0200, Frederic Weisbecker wrote:
> 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?

Its next-20170601: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20170601&id=3ab334ebe84e0dfd1cc3ea2fe77f5ce4406f7370

> Can you give me its HEAD and your config file?

Attached config.

-- 

Thanks,
Sasha

Download attachment "config-sasha.gz" of type "application/gzip" (31104 bytes)