linux-kernel - Re: handling watchdog in SMP

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Message-Id: <17BE975E-6A02-4267-AB8F-5C3B39F485A8@kernel.crashing.org>
Date:	Wed, 23 Apr 2008 08:22:24 -0500
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Wim Van Sebroeck <wim@...ana.be>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: handling watchdog in SMP


On Oct 25, 2007, at 2:37 PM, Wim Van Sebroeck wrote:
> Hi Kumar,
>
>> I was hoping to get some ideas on how to handle the watchdog timers
>> we have on some embedded PPC (booke_wdt.c) cores when we are in a SMP
>> system.
>>
>> The problem is since the watchdog is part of the processor core
>> depending on which processor a given system call is executed at we
>> might get different behavior.  It seems like we would want to mirror
>> the actions to both cores (via smp_call_function).
>>
>> Looking at the file ops we currently support in booke_wdt.c it seems
>> like we could mirror the actions for booke_wdt_write()/booke_wdt_ping
>> () to both cores and ensure when we set something like
>> WDIOC_SETTIMEOUT we set the registers in both processors.
>>
>> I was wondering if anyone had any other ideas or if this model seems
>> to work.
>
> I see 2 ways to go:
> 1) short term: make sure that your actions are duplicated to both  
> cores
> (like you said). At least then you are protected if your complete  
> system
> crashes.
> 2) I'm working on the uniform/generic watchdog device driver. Phase  
> 1 is
> the "new" api and the /dev/watchdog handling. Phase 2 is a sysfs  
> interface.
> Phase 3 is to allow multiple devices (and there I'm still thinking  
> about
> how the /dev/watchdog interface should work).
> But the general idea is to allow at least the control of each watchdog
> device by the sysfs interface.

I haven't been following watchdog subsystem development and was  
wondering if any progress has been made on #2?

- k
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