1 files changed, 60 insertions, 14 deletions

diff --git a/kernel/irq/timings.c b/kernel/irq/timings.c
index 90c735da15d0..19d2fad379ee 100644
--- a/kernel/irq/timings.c
+++ b/kernel/irq/timings.c
@@ -267,6 +267,23 @@ void irq_timings_disable(void)
 #define PREDICTION_MAX		10 /* 2 ^ PREDICTION_MAX useconds */
 #define PREDICTION_BUFFER_SIZE	16 /* slots for EMAs, hardly more than 16 */
 
+/*
+ * Number of elements in the circular buffer: If it happens it was
+ * flushed before, then the number of elements could be smaller than
+ * IRQ_TIMINGS_SIZE, so the count is used, otherwise the array size is
+ * used as we wrapped. The index begins from zero when we did not
+ * wrap. That could be done in a nicer way with the proper circular
+ * array structure type but with the cost of extra computation in the
+ * interrupt handler hot path. We choose efficiency.
+ */
+#define for_each_irqts(i, irqts)					\
+	for (i = irqts->count < IRQ_TIMINGS_SIZE ?			\
+		     0 : irqts->count & IRQ_TIMINGS_MASK,		\
+		     irqts->count = min(IRQ_TIMINGS_SIZE,		\
+					irqts->count);			\
+	     irqts->count > 0; irqts->count--,				\
+		     i = (i + 1) & IRQ_TIMINGS_MASK)
+
 struct irqt_stat {
 	u64	last_ts;
 	u64	ema_time[PREDICTION_BUFFER_SIZE];
@@ -297,7 +314,16 @@ static u64 irq_timings_ema_new(u64 value, u64 ema_old)
 
 static int irq_timings_next_event_index(int *buffer, size_t len, int period_max)
 {
-	int i;
+	int period;
+
+	/*
+	 * Move the beginning pointer to the end minus the max period x 3.
+	 * We are at the point we can begin searching the pattern
+	 */
+	buffer = &buffer[len - (period_max * 3)];
+
+	/* Adjust the length to the maximum allowed period x 3 */
+	len = period_max * 3;
 
 	/*
 	 * The buffer contains the suite of intervals, in a ilog2
@@ -306,21 +332,45 @@ static int irq_timings_next_event_index(int *buffer, size_t len, int period_max)
 	 * period beginning at the end of the buffer. We do that for
 	 * each suffix.
 	 */
-	for (i = period_max; i >= PREDICTION_PERIOD_MIN ; i--) {
+	for (period = period_max; period >= PREDICTION_PERIOD_MIN; period--) {
 
-		int *begin = &buffer[len - (i * 3)];
-		int *ptr = begin;
+		/*
+		 * The first comparison always succeed because the
+		 * suffix is deduced from the first n-period bytes of
+		 * the buffer and we compare the initial suffix with
+		 * itself, so we can skip the first iteration.
+		 */
+		int idx = period;
+		size_t size = period;
 
 		/*
 		 * We look if the suite with period 'i' repeat
 		 * itself. If it is truncated at the end, as it
 		 * repeats we can use the period to find out the next
-		 * element.
+		 * element with the modulo.
 		 */
-		while (!memcmp(ptr, begin, i * sizeof(*ptr))) {
-			ptr += i;
-			if (ptr >= &buffer[len])
-				return begin[((i * 3) % i)];
+		while (!memcmp(buffer, &buffer[idx], size * sizeof(int))) {
+
+			/*
+			 * Move the index in a period basis
+			 */
+			idx += size;
+
+			/*
+			 * If this condition is reached, all previous
+			 * memcmp were successful, so the period is
+			 * found.
+			 */
+			if (idx == len)
+				return buffer[len % period];
+
+			/*
+			 * If the remaining elements to compare are
+			 * smaller than the period, readjust the size
+			 * of the comparison for the last iteration.
+			 */
+			if (len - idx < period)
+				size = len - idx;
 		}
 	}
 
@@ -493,11 +543,7 @@ u64 irq_timings_next_event(u64 now)
 	 * model while decrementing the counter because we consume the
 	 * data from our circular buffer.
 	 */
-
-	i = (irqts->count & IRQ_TIMINGS_MASK) - 1;
-	irqts->count = min(IRQ_TIMINGS_SIZE, irqts->count);
-
-	for (; irqts->count > 0; irqts->count--, i = (i + 1) & IRQ_TIMINGS_MASK) {
+	for_each_irqts(i, irqts) {
 		irq = irq_timing_decode(irqts->values[i], &ts);
 		s = idr_find(&irqt_stats, irq);
 		if (s)