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

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Date:	Thu, 6 Jun 2013 08:30:01 +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>,
	Wim Van Sebroeck <wim@...ana.be>
Cc:	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,
Can you look into below?

On Wed, Jun 5, 2013 at 8:39 AM, anish singh <anish198519851985@...il.com> wrote:
> 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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