From: Tvrtko Ursulin <redacted>

Test that periodic reads of engine busyness against a constant 100% load
are within the 5000ppm tolerance when comparing perf timestamp versus
counter values.

Signed-off-by: Tvrtko Ursulin <redacted>
---
 tests/i915/perf_pmu.c | 46 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 41 insertions(+), 5 deletions(-)

diff --git a/tests/i915/perf_pmu.c b/tests/i915/perf_pmu.c
index 50b5c82bc472..728312be5293 100644
--- a/tests/i915/perf_pmu.c
+++ b/tests/i915/perf_pmu.c

@@ -26,6 +26,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <fcntl.h>
+#include <float.h>
 #include <inttypes.h>
 #include <errno.h>
 #include <signal.h>

@@ -46,6 +47,7 @@
 #include "igt_perf.h"
 #include "igt_sysfs.h"
 #include "igt_pm.h"
+#include "igt_stats.h"
 #include "sw_sync.h"
 
 IGT_TEST_DESCRIPTION("Test the i915 pmu perf interface");

@@ -278,8 +280,11 @@ static void end_spin(int fd, igt_spin_t *spin, unsigned int flags)
 static void
 single(int gem_fd, const struct intel_execution_engine2 *e, unsigned int flags)
 {
+       unsigned int loops = flags & FLAG_LONG ? 20 : 1;
+       double err_min = DBL_MAX, err_max = -DBL_MAX;
        unsigned long slept;
        igt_spin_t *spin;
+       igt_stats_t s;
        uint64_t val;
        int fd;
 

@@ -290,11 +295,40 @@ single(int gem_fd, const struct intel_execution_engine2 *e, unsigned int flags)
        else
                spin = NULL;
 
-       val = pmu_read_single(fd);
-       slept = measured_usleep(batch_duration_ns / 1000);
-       if (flags & TEST_TRAILING_IDLE)
-               end_spin(gem_fd, spin, flags);
-       val = pmu_read_single(fd) - val;
+       igt_stats_init_with_size(&s, loops);
+
+       while (--loops) {