[PATCH-rcu] clocksource: Add a Kconfig option for WATCHDOG_MAX_SKEW

[PATCH-rcu] clocksource: Add a Kconfig option for WATCHDOG_MAX_SKEW

[Waiman Long]

A watchdog maximum skew of 100us may still be too small for
some systems or archs. It may also be too small when some kernel
debug config options are enabled.  So add a new Kconfig option
CLOCKSOURCE_WATCHDOG_MAX_SKEW_US to allow kernel builders to have more
control on the threshold for marking clocksource as unstable.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/time/Kconfig       | 9 +++++++++
 kernel/time/clocksource.c | 8 +++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 04bfd62f5e5c..27b7868b5c30 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -181,5 +181,14 @@ config HIGH_RES_TIMERS
 	  hardware is not capable then this option only increases
 	  the size of the kernel image.
 
+config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
+	int "Clocksource watchdog maximum allowable skew (in μs)"
+	depends on CLOCKSOURCE_WATCHDOG
+	range 50 1000
+	default 100
+	help
+	  Specify the maximum amount of allowable watchdog skew in
+	  microseconds before reporting the clocksource to be unstable.
+
 endmenu
 endif
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index b7e52a642948..877a78bea9b0 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -107,7 +107,13 @@ static u64 suspend_start;
  * This delay could be due to SMIs, NMIs, or to VCPU preemptions.  Used as
  * a lower bound for cs->uncertainty_margin values when registering clocks.
  */
-#define WATCHDOG_MAX_SKEW (100 * NSEC_PER_USEC)
+#ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
+#define MAX_SKEW_USEC	CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
+#else
+#define MAX_SKEW_USEC	100
+#endif
+
+#define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
 
 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
 static void clocksource_watchdog_work(struct work_struct *work);
-- 
2.27.0

Re: [PATCH-rcu] clocksource: Add a Kconfig option for WATCHDOG_MAX_SKEW

[Paul E. McKenney]

On Sun, Dec 05, 2021 at 10:38:15PM -0500, Waiman Long wrote:
> A watchdog maximum skew of 100us may still be too small for
> some systems or archs. It may also be too small when some kernel
> debug config options are enabled.  So add a new Kconfig option
> CLOCKSOURCE_WATCHDOG_MAX_SKEW_US to allow kernel builders to have more
> control on the threshold for marking clocksource as unstable.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>

Queued, thank you!

							Thanx, Paul

> ---
>  kernel/time/Kconfig       | 9 +++++++++
>  kernel/time/clocksource.c | 8 +++++++-
>  2 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
> index 04bfd62f5e5c..27b7868b5c30 100644
> --- a/kernel/time/Kconfig
> +++ b/kernel/time/Kconfig
> @@ -181,5 +181,14 @@ config HIGH_RES_TIMERS
>  	  hardware is not capable then this option only increases
>  	  the size of the kernel image.
>  
> +config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
> +	int "Clocksource watchdog maximum allowable skew (in μs)"
> +	depends on CLOCKSOURCE_WATCHDOG
> +	range 50 1000
> +	default 100
> +	help
> +	  Specify the maximum amount of allowable watchdog skew in
> +	  microseconds before reporting the clocksource to be unstable.
> +
>  endmenu
>  endif
> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> index b7e52a642948..877a78bea9b0 100644
> --- a/kernel/time/clocksource.c
> +++ b/kernel/time/clocksource.c
> @@ -107,7 +107,13 @@ static u64 suspend_start;
>   * This delay could be due to SMIs, NMIs, or to VCPU preemptions.  Used as
>   * a lower bound for cs->uncertainty_margin values when registering clocks.
>   */
> -#define WATCHDOG_MAX_SKEW (100 * NSEC_PER_USEC)
> +#ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
> +#define MAX_SKEW_USEC	CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
> +#else
> +#define MAX_SKEW_USEC	100
> +#endif
> +
> +#define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
>  
>  #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
>  static void clocksource_watchdog_work(struct work_struct *work);
> -- 
> 2.27.0
>