[PATCH] time: Make the clocksource watchdog user configurable

[Gratian Crisan]

The clocksource watchdog is used to detect instabilities in the current
clocksource. This is a beneficial feature on new/unknown hardware however
it can create problems by falsely triggering when the watchdog wraps. The
reason is that an interrupt storm and/or high priority (FIFO/RR) tasks can
preempt the timer softirq long enough for the watchdog to wrap if it has a
limited number of bits available by comparison with the main clocksource.

One observed example is on a Intel Baytrail platform where TSC is the main
clocksource, HPET is disabled due to a hardware bug and acpi_pm gets
selected as the watchdog clocksource.

Provide the option to disable the clocksource watchdog for hardware where
the clocksource stability has been validated.

Signed-off-by: Gratian Crisan <gratian.crisan@xxxxxx>
---
 arch/x86/Kconfig    |  2 +-
 kernel/time/Kconfig | 12 +++++++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2dc18605..6da5d9e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -54,7 +54,7 @@ config X86
 	select CLKEVT_I8253
 	select CLKSRC_I8253			if X86_32
 	select CLOCKSOURCE_VALIDATE_LAST_CYCLE
-	select CLOCKSOURCE_WATCHDOG
+	select HAVE_CLOCKSOURCE_WATCHDOG
 	select CLONE_BACKWARDS			if X86_32
 	select COMPAT_OLD_SIGACTION		if IA32_EMULATION
 	select DCACHE_WORD_ACCESS
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 4008d9f..6707f1d 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -5,7 +5,7 @@
 # Options selectable by arch Kconfig
 
 # Watchdog function for clocksources to detect instabilities
-config CLOCKSOURCE_WATCHDOG
+config HAVE_CLOCKSOURCE_WATCHDOG
 	bool
 
 # Architecture has extra clocksource data
@@ -193,5 +193,15 @@ config HIGH_RES_TIMERS
 	  hardware is not capable then this option only increases
 	  the size of the kernel image.
 
+config CLOCKSOURCE_WATCHDOG
+	bool "Clocksource watchdog"
+	depends on HAVE_CLOCKSOURCE_WATCHDOG
+	default y
+	help
+	  This option enables the watchdog function for clocksources. It is
+	  used to detect instabilities in the currently selected clocksource.
+
+	  Say Y if you are unsure.
+
 endmenu
 endif
-- 
1.9.1