linux-kernel - Re: [RFC PATCH 22/23] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter

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Message-ID: <20180614005839.GA22358@voyager>
Date:   Wed, 13 Jun 2018 17:58:39 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andi Kleen <andi.kleen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Borislav Petkov <bp@...e.de>,
        Tony Luck <tony.luck@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>, x86@...nel.org,
        sparclinux@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Jacob Pan <jacob.jun.pan@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Don Zickus <dzickus@...hat.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Frederic Weisbecker <frederic@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Babu Moger <babu.moger@...cle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Colin Ian King <colin.king@...onical.com>,
        Byungchul Park <byungchul.park@....com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Christoffer Dall <cdall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        David Rientjes <rientjes@...gle.com>,
        iommu@...ts.linux-foundation.org
Subject: Re: [RFC PATCH 22/23] watchdog/hardlockup/hpet: Only enable the HPET
 watchdog via a boot parameter

On Tue, Jun 12, 2018 at 10:26:57PM -0700, Randy Dunlap wrote:
> On 06/12/2018 05:57 PM, Ricardo Neri wrote:
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index f2040d4..a8833c7 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -2577,7 +2577,7 @@
> >  			Format: [state][,regs][,debounce][,die]
> >  
> >  	nmi_watchdog=	[KNL,BUGS=X86] Debugging features for SMP kernels
> > -			Format: [panic,][nopanic,][num]
> > +			Format: [panic,][nopanic,][num,][hpet]
> >  			Valid num: 0 or 1
> >  			0 - turn hardlockup detector in nmi_watchdog off
> >  			1 - turn hardlockup detector in nmi_watchdog on
> 
> This says that I can use "nmi_watchdog=hpet" without using 0 or 1.
> Is that correct?

Yes, this what I meant. In my view, if you set nmi_watchdog=hpet it
implies that you want to activate the NMI watchdog. In this case, perf.

I can see how this will be ambiguous for the case of perf and arch NMI
watchdogs.

Alternative, a new parameter could be added; such as nmi_watchdog_type. I
didn't want to add it in this patchset as I think that a single parameter
can handle the enablement and type of the NMI watchdog.

What do you think?

Thanks and BR,
Ricardo