rt-app: fix calibration issue on mt8173

Calibration sequence fails to get the right ns per loop value when the
calibration is done on the A57 cluster of the mt8173evb.
A new calibration has been added that adds a sleep period between each each
calibration loop. This idle phase enable rt-app to get the to get the right ns
per loop value for such kind of HW.
The calibration sequence finally uses the lowest value of the calibration
methods which match with the highest compute capacity

Reported-by: Koan-Sin Tan <freedom.tan@linaro.org>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>

1 files changed, 75 insertions, 5 deletions

diff --git a/src/rt-app.c b/src/rt-app.c
index 97aee0f..37e9892 100644
--- a/src/rt-app.c
+++ b/src/rt-app.c
@@ -62,12 +62,14 @@ void waste_cpu_cycles(int load_loops)
 }
 
 /*
-* calibrate_cpu_cycles()
-* collects the time that waste_cycles runs.
+* calibrate_cpu_cycles_1()
+* 1st method to calibrate the ns per loop value
+* We alternate idle period and run period in order to not trig some hw
+* protection mechanism like thermal mitgation
 */
-int calibrate_cpu_cycles(int clock)
+int calibrate_cpu_cycles_1(int clock)
 {
-	struct timespec start, stop;
+	struct timespec start, stop, sleep;
 	int max_load_loop = 10000;
 	unsigned int diff;
 	int nsec_per_loop, avg_per_loop = 0;
@@ -75,6 +77,10 @@ int calibrate_cpu_cycles(int clock)
 
 	while (cal_trial) {
 		cal_trial--;
+		sleep.tv_sec = 1;
+		sleep.tv_nsec = 0;
+
+		clock_nanosleep(CLOCK_MONOTONIC, 0, &sleep, NULL);
 
 		clock_gettime(clock, &start);
 		waste_cpu_cycles(max_load_loop);
@@ -100,6 +106,69 @@ int calibrate_cpu_cycles(int clock)
 	return 0;
 }
 
+/*
+* calibrate_cpu_cycles_2()
+* 2nd method to calibrate the ns per loop value
+* We continously runs something to ensure that CPU is set to max freq by the
+* governor
+*/
+int calibrate_cpu_cycles_2(int clock)
+{
+	struct timespec start, stop, sleep;
+	int max_load_loop = 10000;
+	unsigned int diff;
+	int nsec_per_loop, avg_per_loop = 0;
+	int ret, cal_trial = 1000;
+
+	while (cal_trial) {
+		cal_trial--;
+
+		clock_gettime(clock, &start);
+		waste_cpu_cycles(max_load_loop);
+		clock_gettime(clock, &stop);
+
+		diff = (int)timespec_sub_to_ns(&stop, &start);
+		nsec_per_loop = diff / max_load_loop;
+		avg_per_loop = (avg_per_loop + nsec_per_loop) >> 1;
+
+		/* collect a critical mass of samples.*/
+		if ((abs(nsec_per_loop - avg_per_loop) * 50)  < avg_per_loop)
+			return avg_per_loop;
+
+		/*
+		* use several loop duration in order to be sure to not
+		* fall into a specific platform loop duration
+		*(like the cpufreq period)
+		*/
+		/*randomize the number of loops and recheck 1000 times*/
+		max_load_loop += 33333;
+		max_load_loop %= 1000000;
+	}
+	return 0;
+}
+
+/*
+* calibrate_cpu_cycles()
+* Use several methods to calibrate the ns per loop and get the min value which
+* correspond to the highest achievable compute capacity.
+*/
+int calibrate_cpu_cycles(int clock)
+{
+	int calib1, calib2;
+
+	/* Run 1st method */
+	calib1 = calibrate_cpu_cycles_1(clock);
+
+	/* Run 2nd method */
+	calib2 = calibrate_cpu_cycles_2(clock);
+
+	if (calib1 < calib2)
+		return calib1;
+	else
+		return calib2;
+
+}
+
 static inline loadwait(unsigned long exec)
 {
 	unsigned long load_count;
@@ -531,13 +600,14 @@ int main(int argc, char* argv[])
 
 	/* Needs to calibrate 'calib_cpu' core */
 	if (opts.calib_ns_per_loop == 0) {
+		log_notice("Calibrate ns per loop");
 		cpu_set_t calib_set;
 
 		CPU_ZERO(&calib_set);
 		CPU_SET(opts.calib_cpu, &calib_set);
 		sched_getaffinity(0, sizeof(cpu_set_t), &orig_set);
 		sched_setaffinity(0, sizeof(cpu_set_t), &calib_set);
-		p_load = calibrate_cpu_cycles(CLOCK_THREAD_CPUTIME_ID);
+		p_load = calibrate_cpu_cycles(CLOCK_MONOTONIC);
 		sched_setaffinity(0, sizeof(cpu_set_t), &orig_set);
 		log_notice("pLoad = %dns : calib_cpu %d", p_load, opts.calib_cpu);
 	} else {