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

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Message-ID: <20170519131753.sccuu7mksjertzni@redhat.com>
Date:   Fri, 19 May 2017 09:17:53 -0400
From:   Don Zickus <dzickus@...hat.com>
To:     Nicholas Piggin <npiggin@...il.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 Fri, May 19, 2017 at 09:07:31AM +1000, Nicholas Piggin wrote:
> 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.

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