linux-kernel - Re: [RFC] arch hardlockup detector interfaces improvement

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Message-ID: <20170519090731.1e49cd0d@roar.ozlabs.ibm.com>
Date:   Fri, 19 May 2017 09:07:31 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Don Zickus <dzickus@...hat.com>
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        adi-buildroot-devel@...ts.sourceforge.net,
        linux-am33-list@...hat.com, sparclinux@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, uobergfe@...hat.com
Subject: Re: [RFC] arch hardlockup detector interfaces improvement

On Thu, 18 May 2017 12:30:28 -0400
Don Zickus <dzickus@...hat.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.

Thanks,
Nick