linux-kernel - Re: [PATCH] watchdog: store the watchdog sample period as a variable

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Message-ID: <20121204144549.GT76501@redhat.com>
Date:	Tue, 4 Dec 2012 09:45:49 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Chuansheng Liu <chuansheng.liu@...el.com>
Cc:	akpm@...ux-foundation.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog: store the watchdog sample period as a variable

On Tue, Dec 04, 2012 at 06:58:42PM +0800, Chuansheng Liu wrote:
> 
> Currently getting the sample period is always thru complex
> calculation: get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5).
> But just like the watchdog_thresh, which is not changed often.
> 
> So we can store the sample period as a variable, and set it as
> __read_mostly type.

Seems safe and also helps the case of changing the value while running.
Now one has to disable/re-enable the watchdog to utilize the new value.

Acked-by: Don Zickus <dzickus@...hat.com>

> 
> Signed-off-by: liu chuansheng <chuansheng.liu@...el.com>
> ---
>  kernel/watchdog.c |   13 ++++++++-----
>  1 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index dd4b80a..7a32b20 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -31,6 +31,7 @@
>  int watchdog_enabled = 1;
>  int __read_mostly watchdog_thresh = 10;
>  static int __read_mostly watchdog_disabled;
> +static u64 __read_mostly sample_period;
>  
>  static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
>  static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
> @@ -116,7 +117,7 @@ static unsigned long get_timestamp(int this_cpu)
>  	return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */
>  }
>  
> -static u64 get_sample_period(void)
> +static void set_sample_period(void)
>  {
>  	/*
>  	 * convert watchdog_thresh from seconds to ns
> @@ -125,7 +126,7 @@ static u64 get_sample_period(void)
>  	 * and hard thresholds) to increment before the
>  	 * hardlockup detector generates a warning
>  	 */
> -	return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
> +	sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
>  }
>  
>  /* Commands for resetting the watchdog */
> @@ -275,7 +276,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
>  	wake_up_process(__this_cpu_read(softlockup_watchdog));
>  
>  	/* .. and repeat */
> -	hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
> +	hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
>  
>  	if (touch_ts == 0) {
>  		if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
> @@ -356,7 +357,7 @@ static void watchdog_enable(unsigned int cpu)
>  	hrtimer->function = watchdog_timer_fn;
>  
>  	/* done here because hrtimer_start can only pin to smp_processor_id() */
> -	hrtimer_start(hrtimer, ns_to_ktime(get_sample_period()),
> +	hrtimer_start(hrtimer, ns_to_ktime(sample_period),
>  		      HRTIMER_MODE_REL_PINNED);
>  
>  	/* initialize timestamp */
> @@ -383,7 +384,7 @@ static int watchdog_should_run(unsigned int cpu)
>  /*
>   * The watchdog thread function - touches the timestamp.
>   *
> - * It only runs once every get_sample_period() seconds (4 seconds by
> + * It only runs once every sample_period seconds (4 seconds by
>   * default) to reset the softlockup timestamp. If this gets delayed
>   * for more than 2*watchdog_thresh seconds then the debug-printout
>   * triggers in watchdog_timer_fn().
> @@ -516,6 +517,7 @@ int proc_dowatchdog(struct ctl_table *table, int write,
>  	if (ret || !write)
>  		return ret;
>  
> +	set_sample_period();
>  	if (watchdog_enabled && watchdog_thresh)
>  		watchdog_enable_all_cpus();
>  	else
> @@ -537,6 +539,7 @@ static struct smp_hotplug_thread watchdog_threads = {
>  
>  void __init lockup_detector_init(void)
>  {
> +	set_sample_period();
>  	if (smpboot_register_percpu_thread(&watchdog_threads)) {
>  		pr_err("Failed to create watchdog threads, disabled\n");
>  		watchdog_disabled = -ENODEV;
> -- 
> 1.7.0.4
> 
> 
> 
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