[PATCH V3 3/8] genirq/timings: Optimize the period detection speed

From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: tglx@linutronix.de
Cc: linux-kernel@vger.kernel.org, andriy.shevchenko@linux.intel.com
Subject: [PATCH V3 3/8] genirq/timings: Optimize the period detection speed
Date: Mon, 27 May 2019 22:55:16 +0200	[thread overview]
Message-ID: <20190527205521.12091-4-daniel.lezcano@linaro.org> (raw)
In-Reply-To: <20190527205521.12091-1-daniel.lezcano@linaro.org>

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@linaro.org>
---
 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 */
-- 
2.17.1

