linux-kernel - Re: [PATCH] [RFC]Watchdog:core: constant pinging until userspace timesout when delay very less

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Date:	Wed, 5 Jun 2013 08:39:00 +0530
From:	anish singh <anish198519851985@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>, randy.dunlap@...cle.com,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>
Cc:	Wim Van Sebroeck <wim@...ana.be>, linux-watchdog@...r.kernel.org,
	linux-kernel-mail <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RFC]Watchdog:core: constant pinging until userspace
 timesout when delay very less

Hello Wim Van Sabroeck,
Can I get your inputs on this?

On Tue, Jun 4, 2013 at 8:39 AM, anish singh <anish198519851985@...il.com> wrote:
> On Tue, Jun 4, 2013 at 3:55 AM, Guenter Roeck <linux@...ck-us.net> wrote:
>> On Mon, Jun 03, 2013 at 10:23:04PM +0530, anish singh wrote:
>>> On Mon, Jun 3, 2013 at 8:57 PM, Guenter Roeck <linux@...ck-us.net> wrote:
>>> > On Sun, Jun 02, 2013 at 03:43:07PM +0530, anish kumar wrote:
>>> >> Certain watchdog drivers use a timer to keep kicking the watchdog at
>>> >> a rate of 0.5s (HZ/2) untill userspace times out.They do this as
>>> >> we can't guarantee that watchdog will be pinged fast enough
>>> >> for all system loads, especially if timeout is configured for
>>> >> less than or equal to 1 second(basically small values).
>>> >>
>>> >> As suggested by Wim Van Sebroeck & Guenter Roeck we should
>>> >> add this functionality of individual watchdog drivers in the core
>>> >> watchdog core.
>>> >>
>>> >> Signed-off-by: anish kumar <anish198519851985@...il.com>
>>> >
>>> > Not exactly what I had in mind. My idea was to enable the softdog only if
>>> > the hardware watchdog's maximum timeout was low (say, less than a couple
>>> > of minutes), and if a timeout larger than its maximum value was configured.
>>>
>>> watchdog_timeout_invalid wouldn't this check will fail if the user space tries
>>> to set maximum timeout more that what driver can support?It would work
>>> for pika_wdt.c as it is old watchdog driver and doesn't register with watchdog
>>> framwork but new drivers has to pass this api.
>>>
>>> OR
>>>
>>> Do you want to remove this check and go as explained by you?I would
>>> favour this approach though.
>>>
>> One would still have a check, but the enforced limits would no longer be
>> the driver limits, but larger limits implemented in the watchdog core.
> How much larger would be the big question here?Should it be configurable
> property(sysfs?) or some hardcoding based on existing drivers?
>
> Before going for next patch, it would be better for me to wait for some
> more comments.
>>
>>> > In that case, I would have set the hardware watchdog to its maximum value
>>> > and use the softdog to ping it at a rate of, say, 50% of this maximum.
>>> >
>>> > If userspace would not ping the watchdog within its configured value,
>>> > I would stop pinging the hardware watchdog and let it time out.
>>>
>>> One more question.Why is the return value of watchdog_ping int? Anyway
>>> we discard it.
>>
>> I can not answer that question.
>>
>> Guenter
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