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 <anish198519851...@gmail.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.
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.
Guenter
> ---
> 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)
> 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)
> +{
> + 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;
> unsigned int min_timeout;
> unsigned int max_timeout;
> void *driver_data;
> --
> 1.7.10.4
>
>
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