[PATCH 3/9] genirq/timings: Optimize the period detection speed

From: Daniel Lezcano
Date: Mon May 13 2019 - 06:32:07 EST


If we have a minimal period and if there is a period which is a
multiple of it but lesser than the max period then it will be detected
before and the minimal period will be never reached.

1 2 1 2 1 2 1 2 1 2 1 2
<-----> <-----> <----->
<-> <-> <-> <-> <-> <->

In our case, the minimum period is 2 and the maximum period is 5. That
means all repeating pattern of 2 will be detected as repeating pattern
of 4, it is pointless to go up to 2 when searching for the period as it
will always fail.

Remove one loop iteration by increasing the minimal period to 3.

Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
---
kernel/irq/timings.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/irq/timings.c b/kernel/irq/timings.c
index 250bb00ccd85..06bde5253a7d 100644
--- a/kernel/irq/timings.c
+++ b/kernel/irq/timings.c
@@ -261,7 +261,7 @@ void irq_timings_disable(void)
#define EMA_ALPHA_VAL 64
#define EMA_ALPHA_SHIFT 7

-#define PREDICTION_PERIOD_MIN 2
+#define PREDICTION_PERIOD_MIN 3
#define PREDICTION_PERIOD_MAX 5
#define PREDICTION_FACTOR 4
#define PREDICTION_MAX 10 /* 2 ^ PREDICTION_MAX useconds */
--
2.17.1