[tip:irq/core] genirq/timings: Optimize the period detection speed

[tip-bot for Daniel Lezcano]

Commit-ID:  3c2e79f4cef7938125b356e7f5c8fd038212619a
Gitweb:     https://git.kernel.org/tip/3c2e79f4cef7938125b356e7f5c8fd038212619a
Author:     Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
AuthorDate: Mon, 27 May 2019 22:55:16 +0200
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Wed, 12 Jun 2019 10:47:03 +0200

genirq/timings: Optimize the period detection speed

With 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 that 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>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: andriy.shevchenko@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20190527205521.12091-4-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 19d2fad379ee..1d1c411d4cae 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 */