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 21:41:29 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	anish singh <anish198519851985@...il.com>
Cc:	randy.dunlap@...cle.com,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>,
	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

On Thu, Jun 06, 2013 at 08:30:01AM +0530, anish singh wrote:
> Hello Wim Van,
> Can you look into below?
> 
Please be patient. Wim tends to be busy.

Guenter

> 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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