linux-kernel - Re: [PATCH 0/2] nohz: Deal with clock reprogram skipping issues v2

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Date:   Mon, 24 Apr 2017 16:45:23 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Frederic Weisbecker <fweisbec@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...hat.com>,
        James Hartsock <hartsjc@...hat.com>,
        Tim Wright <tim@...bash.co.uk>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 0/2] nohz: Deal with clock reprogram skipping issues v2


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Mon, Apr 24, 2017 at 10:08:35AM +0200, Ingo Molnar wrote:
> > 
> > * Frederic Weisbecker <fweisbec@...il.com> wrote:
> > 
> > > As suggested by Thomas Gleixner, the second patch now integrates
> > > a fix in case the sanity check fails and the clockevent isn't programmed
> > > as expected.
> > > 
> > > Frederic Weisbecker (2):
> > >   nohz: Fix again collision between tick and other hrtimers
> > >   tick: Make sure tick timer is active when bypassing reprogramming
> > > 
> > >  kernel/time/tick-sched.c | 33 ++++++++++++++++++++++++++++++---
> > >  kernel/time/tick-sched.h |  2 ++
> > >  2 files changed, 32 insertions(+), 3 deletions(-)
> > 
> > So I think one of these is causing a new warning on latest -tip:
> > 
> > [  333.341756] ------------[ cut here ]------------
> > [  333.346404] WARNING: CPU: 0 PID: 0 at kernel/time/tick-sched.c:874 __tick_nohz_idle_enter+0x461/0x490
> 
> Oh I'll never be done with that bug :)
> 
> Ok I just booted your config with tip/master and didn't see the warning.
> But the boot seem to be stalled some time after mounting the root fs.
> 
> Can you please try the following patch and tell me what it returns to you?
> 
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index c47d135..6d72e8b 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -872,6 +872,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
>  			goto out;
>  
>  		WARN_ON_ONCE(1);
> +		printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu\n", basemono, ts->next_tick, dev->next_event);
>  	}
>  

Here's what it prints:

[  707.251791] basemono: 706016000000 ts->next_tick: 693216000000 dev->next_event: 706016406127

Full bootlog attached.

Thanks,

	Ingo

View attachment "boot.log" of type "text/plain" (166740 bytes)