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Date: Tue, 27 Jun 2017 16:12:49 -0400
From: Don Zickus <dzickus@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>, Kan Liang <kan.liang@intel.com>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
        akpm@linux-foundation.org, babu.moger@oracle.com, atomlin@redhat.com,
        prarit@redhat.com, torvalds@linux-foundation.org, peterz@infradead.org,
        eranian@google.com, acme@redhat.com, ak@linux.intel.com,
        stable@vger.kernel.org
Subject: Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups
Message-ID: <20170627201249.ll34ecwhpme3vh2u@redhat.com>
References: <20170621144118.5939-1-kan.liang@intel.com>
 <alpine.DEB.2.20.1706212235550.2152@nanos>
 <20170622154450.2lua7fdmigcixldw@redhat.com>
 <alpine.DEB.2.20.1706230952190.2647@nanos>
 <20170623162907.l6inpxgztwwkeaoi@redhat.com>
 <alpine.DEB.2.20.1706232348020.2234@nanos>
 <20170626201927.3ak7fk3yvdzbb4ay@redhat.com>
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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