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

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Date:   Wed, 7 Jun 2017 21:36:45 +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 Wed, Jun 07, 2017 at 04:14:03PM +0200, Frederic Weisbecker wrote:
> On Wed, Jun 07, 2017 at 04:17:41AM +0000, Levin, Alexander (Sasha Levin) wrote:
> > > Thanks Sasha!
> > > 
> > > I couldn't reproduce it, that config boots fine on my kvm.
> > > Would you have the time to dump some traces for me?
> > > 
> > > I'd need you to add this boot option: trace_event=hrtimer_cancel,hrtimer_start,hrtimer_expire_entry
> > > And boot your kernel with the below patch. This will dump the timer traces to your console.
> > > I would be very interested in the resulting console dump file.
> > 
> > Attached. Let me know if you need anything else.
> 
> Great! So now I can deduce that the problem doesn't come from the nohz code as
> ts->next_tick matches the hrtimer deadline. But the dev->next_event from the
> clockevent seems to be out of line.
> 
> Sorry to bother you again, but I'm chasing this bug for several weeks now and
> you're one of the rare person who can reproduce it. So I may need some more
> tracing details.

I take payment in beers ;)

But really, not a problem.

> Here is another version of the debugging patch (not a delta), I added more trace_printk,
> namely the places where we set this dev->next_event. Can you please apply the below and do
> the dump again?

Attached.

-- 

Thanks,
Sasha

Download attachment "log.txt.gz" of type "application/gzip" (46400 bytes)