Millisecond level watchdog interface

Millisecond level watchdog interface

[Corey Minyard]

Hi,

I'm representing the Elisa group, an organization working on making it
easier to use Linux in safety critical applications.

As part of this, one thing we need is a watchdog that has a much finer
granularity than one second.  In some applications, that is just too
long.

Would the watchdog maintainers be ameniable to changes to the interface
to support finer granularity?  Milliseconds should be fine, though higher
resolution would be fine, too.

If so, there are a number of ways you can implement this.  You could
make the interface modal, meaning that you "throw a switch" and the
standard interfaces become millisecond-level.  Or you could create new
ioctls with millisecond level granularity.  You would probably want some
way to fetch the granularity of the timer, too.  Maybe there's another
better way.

Thanks,

-corey

Re: Millisecond level watchdog interface

[Guenter Roeck]

On 6/16/20 9:37 AM, Corey Minyard wrote:
> Hi,
> 
> I'm representing the Elisa group, an organization working on making it
> easier to use Linux in safety critical applications.
> 
> As part of this, one thing we need is a watchdog that has a much finer
> granularity than one second.  In some applications, that is just too
> long.
> 
> Would the watchdog maintainers be ameniable to changes to the interface
> to support finer granularity?  Milliseconds should be fine, though higher
> resolution would be fine, too.
> 
> If so, there are a number of ways you can implement this.  You could
> make the interface modal, meaning that you "throw a switch" and the
> standard interfaces become millisecond-level.  Or you could create new

I would consider that a no-go. We have to be and remain backwards
compatible.

> ioctls with millisecond level granularity.  You would probably want some
> way to fetch the granularity of the timer, too.  Maybe there's another
> better way.
> 

We would have to add a new set of ioctls. Drivers could probably use the
existing API but indicate resolution in struct watchdog_info (something
like WDIOF_RESOLUTION_MS in watchdog_info.options, maybe). I am open
to suggestions.

Guenter