On Fri, May 19, 2017 at 09:07:31AM +1000, Nicholas Piggin wrote:

On Thu, 18 May 2017 12:30:28 -0400
Don Zickus [off-list ref] wrote:

quoted

(adding Uli)

On Fri, May 19, 2017 at 01:50:26AM +1000, Nicholas Piggin wrote:

quoted

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.

quoted

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