RE: [PATCH V2] kernel/watchdog: fix spurious hard lockups

[Liang, Kan]

> 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?
> 

I haven't heard back any test result yet.

The above patch looks good to me.
But I'm not sure if /10 is enough. We may need /15.
Anyway, I think we will test /10 first.

Which workaround do you prefer, the above one or the one checking timestamp?


Thanks,
Kan