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

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Date:   Wed, 13 Jun 2018 20:30:00 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
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 06/13/2018 05:58 PM, Ricardo Neri wrote:
> 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?

I think it's OK like it is.

thanks,
-- 
~Randy