linux-kernel - Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups

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Message-ID: <20170627201249.ll34ecwhpme3vh2u@redhat.com>
Date:   Tue, 27 Jun 2017 16:12:49 -0400
From:   Don Zickus <dzickus@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Kan Liang <kan.liang@...el.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        akpm@...ux-foundation.org, babu.moger@...cle.com,
        atomlin@...hat.com, prarit@...hat.com,
        torvalds@...ux-foundation.org, peterz@...radead.org,
        eranian@...gle.com, acme@...hat.com, ak@...ux.intel.com,
        stable@...r.kernel.org
Subject: Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups

On Mon, Jun 26, 2017 at 04:19:27PM -0400, Don Zickus wrote:
> On Fri, Jun 23, 2017 at 11:50:25PM +0200, Thomas Gleixner wrote:
> > On Fri, 23 Jun 2017, Don Zickus wrote:
> > > Hmm, all this work for a temp fix.  Kan, how much longer until the real fix
> > > of having perf count the right cycles?
> > 
> > Quite a while. The approach is wilfully breaking the user space ABI, which
> > is not going to happen.
> > 
> > And there is a simpler solution as well, as I said here:
> > 
> >     http://lkml.kernel.org/r/alpine.DEB.2.20.1706221730520.1885@nanos
> 
> Hi Thomas,
> 
> So, you are saying instead of slowing down the perf counter, speed up the
> hrtimer to sample more frequently like so:
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 03e0b69..8ff49de 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -160,7 +160,7 @@ static void set_sample_period(void)
>  	 * and hard thresholds) to increment before the
>  	 * hardlockup detector generates a warning
>  	 */
> -	sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
> +	sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 10);
>  }

Hi Kan,

Will the above patch work for you?

Cheers,
Don