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

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Date:	Mon, 3 Jun 2013 08:27:25 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	anish kumar <anish198519851985@...il.com>
Cc:	wim@...ana.be, linux-watchdog@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC]Watchdog:core: constant pinging until userspace
 timesout when delay very less

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.
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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