[RFC][PATCH 1/4] clocksource: Add optional cs::mark_unstable() method

From: Peter Zijlstra
Date: Thu Dec 15 2016 - 08:13:30 EST


From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

PeterZ reported that we'd fail to mark the TSC unstable when the
clocksource watchdog finds it unsuitable.

Allow a clocksource to run a custom action when its being marked
unstable and hook up the TSC unstable code.

Reported-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/x86/kernel/tsc.c | 11 +++++++++++
include/linux/clocksource.h | 3 +++
kernel/time/clocksource.c | 4 ++++
3 files changed, 18 insertions(+)

--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1101,6 +1101,16 @@ static cycle_t read_tsc(struct clocksour
return (cycle_t)rdtsc_ordered();
}

+static void tsc_cs_mark_unstable(struct clocksource *cs)
+{
+ if (tsc_unstable)
+ return;
+ tsc_unstable = 1;
+ clear_sched_clock_stable();
+ disable_sched_clock_irqtime();
+ pr_info("Marking TSC unstable due to clocksource watchdog\n");
+}
+
/*
* .mask MUST be CLOCKSOURCE_MASK(64). See comment above read_tsc()
*/
@@ -1112,6 +1122,7 @@ static struct clocksource clocksource_ts
.flags = CLOCK_SOURCE_IS_CONTINUOUS |
CLOCK_SOURCE_MUST_VERIFY,
.archdata = { .vclock_mode = VCLOCK_TSC },
+ .mark_unstable = tsc_cs_mark_unstable,
};

void mark_tsc_unstable(char *reason)
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -62,6 +62,8 @@ struct module;
* @archdata: arch-specific data
* @suspend: suspend function for the clocksource, if necessary
* @resume: resume function for the clocksource, if necessary
+ * @mark_unstable: Optional function to inform the clocksource driver that
+ * the watchdog marked the clocksource unstable
* @owner: module reference, must be set by clocksource in modules
*
* Note: This struct is not used in hotpathes of the timekeeping code
@@ -93,6 +95,7 @@ struct clocksource {
unsigned long flags;
void (*suspend)(struct clocksource *cs);
void (*resume)(struct clocksource *cs);
+ void (*mark_unstable)(struct clocksource *cs);

/* private: */
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -140,6 +140,10 @@ static void __clocksource_unstable(struc
{
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
cs->flags |= CLOCK_SOURCE_UNSTABLE;
+
+ if (cs->mark_unstable)
+ cs->mark_unstable(cs);
+
if (finished_booting)
schedule_work(&watchdog_work);
}