linux-kernel - Re: handling watchdog in SMP

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Date:	Thu, 25 Oct 2007 21:37:02 +0200
From:	Wim Van Sebroeck <wim@...ana.be>
To:	Kumar Gala <galak@...nel.crashing.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: handling watchdog in SMP

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.

Greetings,
Wim.

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