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

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Message-ID: <CAK7N6vqUM+NovH_vtf40OeKstzRrTM2FOZb+cp-nq0k6vVtjag@mail.gmail.com>
Date:	Mon, 3 Jun 2013 20:08:24 +0530
From:	anish singh <anish198519851985@...il.com>
To:	Wim Van Sebroeck <wim@...ana.be>,
	Guenter Roeck <linux@...ck-us.net>
Cc:	linux-watchdog@...r.kernel.org,
	linux-kernel-mail <linux-kernel@...r.kernel.org>,
	anish kumar <anish198519851985@...il.com>
Subject: Re: [PATCH] [RFC]Watchdog:core: constant pinging until userspace
 timesout when delay very less

any inputs?

On Sun, Jun 2, 2013 at 3:56 PM, anish singh <anish198519851985@...il.com> wrote:
> On Sun, Jun 2, 2013 at 3:43 PM, anish kumar <anish198519851985@...il.com> 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>
>> ---
>>  drivers/watchdog/watchdog_dev.c |   34 +++++++++++++++++++++++++++++-----
>>  include/linux/watchdog.h        |    1 +
>>  2 files changed, 30 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
>> index faf4e18..0305803 100644
>> --- a/drivers/watchdog/watchdog_dev.c
>> +++ b/drivers/watchdog/watchdog_dev.c
>> @@ -41,9 +41,14 @@
>>  #include <linux/miscdevice.h>  /* For handling misc devices */
>>  #include <linux/init.h>                /* For __init/__exit/... */
>>  #include <linux/uaccess.h>     /* For copy_to_user/put_user/... */
>> +#include <linux/timer.h>
>> +#include <linux/jiffies.h>
>>
>>  #include "watchdog_core.h"
>>
>> +/* Timer heartbeat (500ms) */
>> +#define WDT_TIMEOUT    (HZ/2) /* should this be sysfs? */
>> +
>>  /* the dev_t structure to store the dynamically allocated watchdog devices */
>>  static dev_t watchdog_devt;
>>  /* the watchdog device behind /dev/watchdog */
>> @@ -73,16 +78,33 @@ static int watchdog_ping(struct watchdog_device *wddev)
> I think watchdog_ping function prototype should be changed as nowhere
> we use the return value.
>>         if (!watchdog_active(wddev))
>>                 goto out_ping;
>>
>> -       if (wddev->ops->ping)
>> -               err = wddev->ops->ping(wddev);  /* ping the watchdog */
>> -       else
>> -               err = wddev->ops->start(wddev); /* restart watchdog */
>> +       /* should we check ping interval value i.e. timeout value
>> +          if it is less than certain threshold then only we
>> +          should add this logic of periodic pinging? */
>> +       if (time_before(jiffies, (unsigned long)wddev->timeout)) {
>> +               if (wddev->ops->ping)
>> +                       err = wddev->ops->ping(wddev);/* ping the watchdog */
>> +               else
>> +                       err = wddev->ops->start(wddev);/* restart watchdog */
>> +               mod_timer(&wddev->timer, jiffies + WDT_TIMEOUT);
>> +       } else {
>> +               /*
>> +                *what we should when we find out that userspace
>> +                *has timed out?
>> +                **/
>> +       }
>>
>>  out_ping:
>>         mutex_unlock(&wddev->lock);
>>         return err;
>>  }
>>
>> +static void watchdog_ping_wrapper(unsigned long priv)
> if we change the watchdog_ping api then we don't need this wrapper.
>> +{
>> +       struct watchdog_device *wdd = (void *)priv;
>> +       watchdog_ping(wdd);
>> +}
>> +
>>  /*
>>   *     watchdog_start: wrapper to start the watchdog.
>>   *     @wddev: the watchdog device to start
>> @@ -109,7 +131,8 @@ static int watchdog_start(struct watchdog_device *wddev)
>>         err = wddev->ops->start(wddev);
>>         if (err == 0)
>>                 set_bit(WDOG_ACTIVE, &wddev->status);
>> -
>> +
>> +       mod_timer(&wddev->timer, jiffies + WDT_TIMEOUT);
>>  out_start:
>>         mutex_unlock(&wddev->lock);
>>         return err;
>> @@ -552,6 +575,7 @@ int watchdog_dev_register(struct watchdog_device *watchdog)
>>                         old_wdd = NULL;
>>                 }
>>         }
>> +       setup_timer(&watchdog->timer, 0, (long)watchdog_ping_wrapper);
>>         return err;
>>  }
>>
>> diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
>> index 2a3038e..e5f18f7 100644
>> --- a/include/linux/watchdog.h
>> +++ b/include/linux/watchdog.h
>> @@ -84,6 +84,7 @@ struct watchdog_device {
>>         const struct watchdog_ops *ops;
>>         unsigned int bootstatus;
>>         unsigned int timeout;
>> +       struct timer_list timer;
> should we use hrtimer? or timer would do?
>>         unsigned int min_timeout;
>>         unsigned int max_timeout;
>>         void *driver_data;
>> --
>> 1.7.10.4
>>
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