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-rw-r--r--kernel/irq/timings.c51
1 files changed, 42 insertions, 9 deletions
diff --git a/kernel/irq/timings.c b/kernel/irq/timings.c
index 90c735da15d0..4f5daf3db13b 100644
--- a/kernel/irq/timings.c
+++ b/kernel/irq/timings.c
@@ -297,7 +297,16 @@ 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 +315,45 @@ 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;
}
}