lkml.org 
[lkml]   [2015]   [Apr]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v1] watchdog: Use a reference cycle counter to avoid scaling issues
On Thu, Apr 23, 2015 at 10:01:04PM +0200, Thomas Gleixner wrote:
> On Thu, 23 Apr 2015, Alexander Shishkin wrote:
>
> > The problem with using cycle counter for NMI watchdog is that its
> > frequency changes with the corresponding core's frequency. This means
> > that, in particular, if the core frequency scales up, watchdog NMI will
> > arrive more frequently than what user requested through watchdog_thresh
> > and also increasing the probability of setting off the hardlockup detector,
> > because the corresponding hrtimer will keep firing at the same intervals
> > regardless of the core frequency. And, if the core can turbo to up to 2.5x
> > its base frequency (and therefore TSC) [1], we'll have the hrtimer and NMI
>
> So you are saying that this M-5Y10 has a non-constant TSC again? You
> really can't be serious about that.

The TSC is constant, but the maximum frequency can be >=2.5TSC, so the
watchdog which uses cycles can have that much error.

-Andi

--
ak@linux.intel.com -- Speaking for myself only


\
 
 \ /
  Last update: 2015-04-23 22:41    [W:0.062 / U:0.908 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site