1 files changed, 65 insertions, 34 deletions

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index b3466d4e0cc2..7713b2b53f61 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -86,6 +86,30 @@ void sched_clock_init(void)
 static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable);
 static int __sched_clock_stable_early;
 
+/*
+ * We want: ktime_get_ns() + gtod_offset == sched_clock() + raw_offset
+ */
+static __read_mostly u64 raw_offset;
+static __read_mostly u64 gtod_offset;
+
+struct sched_clock_data {
+	u64			tick_raw;
+	u64			tick_gtod;
+	u64			clock;
+};
+
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
+
+static inline struct sched_clock_data *this_scd(void)
+{
+	return this_cpu_ptr(&sched_clock_data);
+}
+
+static inline struct sched_clock_data *cpu_sdc(int cpu)
+{
+	return &per_cpu(sched_clock_data, cpu);
+}
+
 int sched_clock_stable(void)
 {
 	return static_branch_likely(&__sched_clock_stable);
@@ -93,6 +117,17 @@ int sched_clock_stable(void)
 
 static void __set_sched_clock_stable(void)
 {
+	struct sched_clock_data *scd = this_scd();
+
+	/*
+	 * Attempt to make the (initial) unstable->stable transition continuous.
+	 */
+	raw_offset = (scd->tick_gtod + gtod_offset) - (scd->tick_raw);
+
+	printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n",
+			scd->tick_gtod, gtod_offset,
+			scd->tick_raw,  raw_offset);
+
 	static_branch_enable(&__sched_clock_stable);
 	tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);
 }
@@ -117,7 +152,23 @@ void set_sched_clock_stable(void)
 
 static void __clear_sched_clock_stable(struct work_struct *work)
 {
-	/* XXX worry about clock continuity */
+	struct sched_clock_data *scd = this_scd();
+
+	/*
+	 * Attempt to make the stable->unstable transition continuous.
+	 *
+	 * Trouble is, this is typically called from the TSC watchdog
+	 * timer, which is late per definition. This means the tick
+	 * values can already be screwy.
+	 *
+	 * Still do what we can.
+	 */
+	gtod_offset = (scd->tick_raw + raw_offset) - (scd->tick_gtod);
+
+	printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n",
+			scd->tick_gtod, gtod_offset,
+			scd->tick_raw,  raw_offset);
+
 	static_branch_disable(&__sched_clock_stable);
 	tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
 }
@@ -134,28 +185,9 @@ void clear_sched_clock_stable(void)
 		schedule_work(&sched_clock_work);
 }
 
-struct sched_clock_data {
-	u64			tick_raw;
-	u64			tick_gtod;
-	u64			clock;
-};
-
-static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
-
-static inline struct sched_clock_data *this_scd(void)
-{
-	return this_cpu_ptr(&sched_clock_data);
-}
-
-static inline struct sched_clock_data *cpu_sdc(int cpu)
-{
-	return &per_cpu(sched_clock_data, cpu);
-}
-
 void sched_clock_init_late(void)
 {
 	sched_clock_running = 2;
-
 	/*
 	 * Ensure that it is impossible to not do a static_key update.
 	 *
@@ -210,7 +242,7 @@ again:
 	 *		      scd->tick_gtod + TICK_NSEC);
 	 */
 
-	clock = scd->tick_gtod + delta;
+	clock = scd->tick_gtod + gtod_offset + delta;
 	min_clock = wrap_max(scd->tick_gtod, old_clock);
 	max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
 
@@ -296,7 +328,7 @@ u64 sched_clock_cpu(int cpu)
 	u64 clock;
 
 	if (sched_clock_stable())
-		return sched_clock();
+		return sched_clock() + raw_offset;
 
 	if (unlikely(!sched_clock_running))
 		return 0ull;
@@ -317,23 +349,22 @@ EXPORT_SYMBOL_GPL(sched_clock_cpu);
 void sched_clock_tick(void)
 {
 	struct sched_clock_data *scd;
-	u64 now, now_gtod;
-
-	if (sched_clock_stable())
-		return;
-
-	if (unlikely(!sched_clock_running))
-		return;
 
 	WARN_ON_ONCE(!irqs_disabled());
 
+	/*
+	 * Update these values even if sched_clock_stable(), because it can
+	 * become unstable at any point in time at which point we need some
+	 * values to fall back on.
+	 *
+	 * XXX arguably we can skip this if we expose tsc_clocksource_reliable
+	 */
 	scd = this_scd();
-	now_gtod = ktime_to_ns(ktime_get());
-	now = sched_clock();
+	scd->tick_raw  = sched_clock();
+	scd->tick_gtod = ktime_get_ns();
 
-	scd->tick_raw = now;
-	scd->tick_gtod = now_gtod;
-	sched_clock_local(scd);
+	if (!sched_clock_stable() && likely(sched_clock_running))
+		sched_clock_local(scd);
 }
 
 /*