[PATCH 21/21] time: Rework debugging variables so they aren't global

[John Stultz]

Ingo suggested that the timekeeping debugging variables
recently added should not be global, and should be tied
to the timekeeper's read_base.

Thus this patch implements that suggestion.

I'm a little hesitant here, since the tkr structure
has been carefully designed to fit in a cacheline.
However, these additions are all at the end of the
structure and are conditionally compiled.

Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: Richard Cochran <richardcochran@xxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
 include/linux/timekeeper_internal.h | 18 +++++++++++++++++-
 kernel/time/timekeeping.c           | 33 ++++++++++-----------------------
 2 files changed, 27 insertions(+), 24 deletions(-)

diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index fb86963..9b33027 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -20,9 +20,13 @@
  * @shift:	Shift value for scaled math conversion
  * @xtime_nsec: Shifted (fractional) nano seconds offset for readout
  * @base:	ktime_t (nanoseconds) base time for readout
+ * @last_warning:   Warning ratelimiter (DEBUG_TIMEKEEPING)
+ * @underflow_seen: Underflow warning flag (DEBUG_TIMEKEEPING)
+ * @overflow_seen:  Overflow warning flag (DEBUG_TIMEKEEPING)
  *
  * This struct has size 56 byte on 64 bit. Together with a seqcount it
- * occupies a single 64byte cache line.
+ * occupies a single 64byte cache line (when DEBUG_TIMEKEEPING is not
+ * enabled).
  *
  * The struct is separate from struct timekeeper as it is also used
  * for a fast NMI safe accessors.
@@ -36,6 +40,18 @@ struct tk_read_base {
 	u32			shift;
 	u64			xtime_nsec;
 	ktime_t			base;
+#ifdef CONFIG_DEBUG_TIMEKEEPING
+	long			last_warning;
+	/*
+	 * These simple flag variables are managed
+	 * without locks, which is racy, but ok since
+	 * we don't really care about being super
+	 * precise about how many events were seen,
+	 * just that a problem was observed.
+	 */
+	int			underflow_seen;
+	int			overflow_seen;
+#endif
 };
 
 /**
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 676896e..ad7a80f 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -118,19 +118,6 @@ static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta)
 
 #ifdef CONFIG_DEBUG_TIMEKEEPING
 #define WARNING_FREQ (HZ*300) /* 5 minute rate-limiting */
-/*
- * These simple flag variables are managed
- * without locks, which is racy, but ok since
- * we don't really care about being super
- * precise about how many events were seen,
- * just that a problem was observed.
- */
-static int timekeeping_underflow_seen;
-static int timekeeping_overflow_seen;
-
-/* last_warning is only modified under the timekeeping lock */
-static long timekeeping_last_warning;
-
 static void timekeeping_check_update(struct tk_read_base *tkr, cycle_t offset)
 {
 
@@ -149,24 +136,24 @@ static void timekeeping_check_update(struct tk_read_base *tkr, cycle_t offset)
 		}
 	}
 
-	if (timekeeping_underflow_seen) {
-		if (jiffies - timekeeping_last_warning > WARNING_FREQ) {
+	if (tkr->underflow_seen) {
+		if (jiffies - tkr->last_warning > WARNING_FREQ) {
 			printk_deferred("WARNING: Underflow in clocksource '%s' observed, time update ignored.\n", name);
 			printk_deferred("         Please report this, consider using a different clocksource, if possible.\n");
 			printk_deferred("         Your kernel is probably still fine.\n");
-			timekeeping_last_warning = jiffies;
+			tkr->last_warning = jiffies;
 		}
-		timekeeping_underflow_seen = 0;
+		tkr->underflow_seen = 0;
 	}
 
-	if (timekeeping_overflow_seen) {
-		if (jiffies - timekeeping_last_warning > WARNING_FREQ) {
+	if (tkr->overflow_seen) {
+		if (jiffies - tkr->last_warning > WARNING_FREQ) {
 			printk_deferred("WARNING: Overflow in clocksource '%s' observed, time update capped.\n", name);
 			printk_deferred("         Please report this, consider using a different clocksource, if possible.\n");
 			printk_deferred("         Your kernel is probably still fine.\n");
-			timekeeping_last_warning = jiffies;
+			tkr->last_warning = jiffies;
 		}
-		timekeeping_overflow_seen = 0;
+		tkr->overflow_seen = 0;
 	}
 }
 
@@ -197,13 +184,13 @@ static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr)
 	 * mask-relative negative values.
 	 */
 	if (unlikely((~delta & mask) < (mask >> 3))) {
-		timekeeping_underflow_seen = 1;
+		tkr->underflow_seen = 1;
 		delta = 0;
 	}
 
 	/* Cap delta value to the max_cycles values to avoid mult overflows */
 	if (unlikely(delta > max)) {
-		timekeeping_overflow_seen = 1;
+		tkr->overflow_seen = 1;
 		delta = tkr->clock->max_cycles;
 	}
 
-- 
1.9.1

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