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SubjectRe: [RFC] arch hardlockup detector interfaces improvement
On Fri, May 19, 2017 at 09:07:31AM +1000, Nicholas Piggin wrote:
> On Thu, 18 May 2017 12:30:28 -0400
> Don Zickus <dzickus@redhat.com> wrote:
>
> > (adding Uli)
> >
> > On Fri, May 19, 2017 at 01:50:26AM +1000, Nicholas Piggin wrote:
> > > I'd like to make it easier for architectures that have their own NMI /
> > > hard lockup detector to reuse various configuration interfaces that are
> > > provided by generic detectors (cmdline, sysctl, suspend/resume calls).
> > >
> > > I'd also like to remove the dependency of arch hard lockup detectors
> > > on the softlockup detector. The reason being these watchdogs can be
> > > very small (sparc's is like a page of core code that does not use any
> > > big subsystem like kthreads or timers).
> > >
> > > So I do this by adding a separate CONFIG_SOFTLOCKUP_DETECTOR, and
> > > juggling around what goes under config options. HAVE_NMI_WATCHDOG
> > > continues to be the config for arch to override the hard lockup
> > > detector, which is expanded to cover a few more cases.
> >
> > Basically you are trying to remove the heavy HARDLOCKUP pieces to minimize
> > the SOFTLOCKUP piece and use your own NMI detector, right?
> >
> > I am guessing you would then disable SOFTLOCKUP to remove all the kthread
> > and timer stuff but continue to use the generic infrastructure to help
> > manager your own NMI detector?
>
> Yes that's right.
>
> > A lot of the code is just re-organizing things and adding an explicit
> > ifdef on SOFTLOCKUP, which seems fine to me.
> >
> > I just need to spend some time on some of your #else clauses to see what
> > functionality is dropped when you use your approach.
>
> Okay, appreciated. I can trim down cc lists and send you my powerpc
> WIP if you'd like to have a look.

I am curious to know what IBM thinks there. Currently the HARDLOCKUP
detector sits on top of perf. I get the impression, you are removing that
dependency. Is that a permanent thing or are you thinking of switching back
and forth depending on if SOFTLOCKUP is enabled or not?

Cheers,
Don

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