diff options
| -rw-r--r-- | drivers/cpuidle/governors/menu.c | 35 |
1 files changed, 17 insertions, 18 deletions
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c index 0742b3296673..beef7ae123ba 100644 --- a/drivers/cpuidle/governors/menu.c +++ b/drivers/cpuidle/governors/menu.c @@ -200,7 +200,7 @@ static void get_typical_interval(struct menu_device *data) { int i, divisor; unsigned int max, thresh; - uint64_t avg, stddev; + uint64_t avg, variance; thresh = UINT_MAX; /* Discard outliers above this value */ @@ -224,36 +224,35 @@ again: else do_div(avg, divisor); - /* Then try to determine standard deviation */ - stddev = 0; + /* Then try to determine variance */ + variance = 0; for (i = 0; i < INTERVALS; i++) { unsigned int value = data->intervals[i]; if (value <= thresh) { int64_t diff = value - avg; - stddev += diff * diff; + variance += diff * diff; } } if (divisor == INTERVALS) - stddev >>= INTERVAL_SHIFT; + variance >>= INTERVAL_SHIFT; else - do_div(stddev, divisor); + do_div(variance, divisor); /* - * The typical interval is obtained when standard deviation is small - * or standard deviation is small compared to the average interval. - * - * int_sqrt() formal parameter type is unsigned long. When the - * greatest difference to an outlier exceeds ~65 ms * sqrt(divisor) - * the resulting squared standard deviation exceeds the input domain - * of int_sqrt on platforms where unsigned long is 32 bits in size. - * In such case reject the candidate average. + * The typical interval is obtained when standard deviation is + * small (stddev <= 20 us, variance <= 400 us^2) or standard + * deviation is small compared to the average interval (avg > + * 6*stddev, avg^2 > 36*variance). The average is smaller than + * UINT_MAX aka U32_MAX, so computing its square does not + * overflow a u64. We simply reject this candidate average if + * the standard deviation is greater than 715 s (which is + * rather unlikely). * * Use this result only if there is no timer to wake us up sooner. */ - if (likely(stddev <= ULONG_MAX)) { - stddev = int_sqrt(stddev); - if (((avg > stddev * 6) && (divisor * 4 >= INTERVALS * 3)) - || stddev <= 20) { + if (likely(variance <= U64_MAX/36)) { + if (((avg*avg > variance*36) && (divisor * 4 >= INTERVALS * 3)) + || variance <= 400) { if (data->next_timer_us > avg) data->predicted_us = avg; return; |