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

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups
Date	2017-06-26 22:40 +0200
Message-ID	<tWIXE-72s-19@gated-at.bofh.it> (permalink)
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On Mon, 26 Jun 2017, 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);
>  }
> 
>  /* Commands for resetting the watchdog */
> 
> 
> That is another way of doing it.  It just hits all the arches.  It does seem
> cleaner as the watchdog_thresh value still retains it correct meaning.  Are
> the laptop folks going to yell at me some more for waking their systems up
> more? :-)

Yes, that's bound to happen. You might make them less angry if you wake the
softlockup thread only on every second hrtimer expiry, i.e. keeping the
current wakeup rate.  But I can't promise that this will significantly
lower their wrath. :)

Thanks,

	tglx

Thread

[PATCH V2] kernel/watchdog: fix spurious hard lockups kan.liang@intel.com - 2017-06-21 16:50 +0200
  Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-21 17:20 +0200
    RE: [PATCH V2] kernel/watchdog: fix spurious hard lockups "Liang, Kan" <kan.liang@intel.com> - 2017-06-21 19:10 +0200
      Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Prarit Bhargava <prarit@redhat.com> - 2017-06-21 19:50 +0200
    Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Andi Kleen <ak@linux.intel.com> - 2017-06-21 19:10 +0200
      Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-21 22:10 +0200
  Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-22 00:00 +0200
    Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-22 17:40 +0200
    Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-22 17:50 +0200
      RE: [PATCH V2] kernel/watchdog: fix spurious hard lockups "Liang, Kan" <kan.liang@intel.com> - 2017-06-22 18:00 +0200
      Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-23 10:10 +0200
        Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-23 18:30 +0200
          Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-24 00:00 +0200
            Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-26 22:30 +0200
              Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-26 22:40 +0200
              Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-27 22:20 +0200
                RE: [PATCH V2] kernel/watchdog: fix spurious hard lockups "Liang, Kan" <kan.liang@intel.com> - 2017-06-27 22:50 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-27 23:10 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Andi Kleen <ak@linux.intel.com> - 2017-06-28 01:50 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-28 21:10 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Andi Kleen <ak@linux.intel.com> - 2017-06-28 22:20 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-29 17:50 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Andi Kleen <ak@linux.intel.com> - 2017-06-29 18:20 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-29 18:30 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Andi Kleen <ak@linux.intel.com> - 2017-06-29 18:40 +0200

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