[igt-dev] [PATCH i-g-t 2/2] tests/perf_pmu: Verify engine busyness accuracy

[Tvrtko Ursulin <tursulin@ursulin.net>]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

A subtest to verify that the engine busyness is reported with expected
accuracy on platforms where the feature is available.

We test three patterns: 2%, 50% and 98% load per engine.

v2:
 * Use spin batch instead of nop calibration.
 * Various tweaks.

v3:
 * Change loops to be time based.
 * Use __igt_spin_batch_new inside timing sensitive loops.
 * Fixed PWM sleep handling.

v4:
 * Use restarting spin batch.
 * Calibrate more carefully by looking at the real PWM loop.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
 tests/perf_pmu.c | 167 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 167 insertions(+)

diff --git a/tests/perf_pmu.c b/tests/perf_pmu.c
index 2f7d33414a53..ffba750ef3a5 100644
--- a/tests/perf_pmu.c
+++ b/tests/perf_pmu.c
@@ -35,6 +35,7 @@
 #include <dirent.h>
 #include <time.h>
 #include <poll.h>
+#include <sched.h>
 
 #include "igt.h"
 #include "igt_core.h"
@@ -1169,6 +1170,162 @@ test_rc6(int gem_fd)
 	assert_within_epsilon(busy - prev, 0.0, tolerance);
 }
 
+static uint64_t __pmu_read_single(int fd, uint64_t *ts)
+{
+	uint64_t data[2];
+
+	igt_assert_eq(read(fd, data, sizeof(data)), sizeof(data));
+
+	*ts = data[1];
+
+	return data[0];
+}
+
+static double __error(double val, double ref)
+{
+	igt_assert(ref != 0.0);
+	return (100.0 * val / ref) - 100.0;
+}
+
+static void debug_error(const char *str, double val, double ref)
+{
+	igt_debug("%s=%.2f%% (%.2f/%.2f)\n", str, __error(val, ref), val, ref);
+}
+
+static void log_error(const char *str, double val, double ref)
+{
+	debug_error(str, val, ref);
+	igt_info("%s=%.2f%%\n", str, __error(val, ref));
+}
+
+#define div_round_up(a, b) (((a) + (b) - 1) / (b))
+
+static void
+accuracy(int gem_fd, const struct intel_execution_engine2 *e,
+	 unsigned long target_busy_pct)
+{
+	const unsigned int min_test_loops = 7;
+	const unsigned long min_test_us = 1e6;
+	unsigned long busy_us = 2500;
+	unsigned long idle_us = 100 * (busy_us - target_busy_pct *
+				busy_us / 100) / target_busy_pct;
+	unsigned long pwm_calibration_us;
+	unsigned long test_us;
+	double busy_r;
+	uint64_t val[2];
+	uint64_t ts[2];
+	int fd;
+
+	/* Sampling platforms cannot reach the high accuracy criteria. */
+	igt_require(intel_gen(intel_get_drm_devid(gem_fd)) >= 8);
+
+	while (idle_us < 2500) {
+		busy_us *= 2;
+		idle_us *= 2;
+	}
+
+	pwm_calibration_us = min_test_loops * (busy_us + idle_us);
+	while (pwm_calibration_us < min_test_us)
+		pwm_calibration_us += busy_us + idle_us;
+	test_us = min_test_loops * (idle_us + busy_us);
+	while (test_us < min_test_us)
+		test_us += busy_us + idle_us;
+
+	igt_info("calibration=%luus, test=%luus; busy=%luus, idle=%luus\n",
+		 pwm_calibration_us, test_us, busy_us, idle_us);
+
+	assert_within_epsilon((double)busy_us / (busy_us + idle_us),
+				(double)target_busy_pct / 100.0, tolerance);
+
+	/* Emit PWM pattern on the engine from a child. */
+	igt_fork(child, 1) {
+		struct sched_param rt = { .sched_priority = 99 };
+		const unsigned long timeout[] = { pwm_calibration_us * 1000,
+						  test_us * 2 * 1000 };
+		unsigned long sleep_busy = busy_us;
+		unsigned long sleep_idle = idle_us;
+		igt_spin_t *spin;
+
+		/* We need the best sleep accuracy we can get. */
+		igt_require(sched_setscheduler(0,
+					       SCHED_FIFO | SCHED_RESET_ON_FORK,
+					       &rt) == 0);
+
+		/* Allocate our spin batch and idle it. */
+		spin = igt_spin_batch_new(gem_fd, 0, e2ring(gem_fd, e), 0);
+		igt_spin_batch_end(spin);
+		gem_sync(gem_fd, spin->handle);
+
+		/* 1st pass is calibration, second pass is the test. */
+		for (int pass = 0; pass < ARRAY_SIZE(timeout); pass++) {
+			unsigned long busy_ns = 0, idle_ns = 0;
+			struct timespec test_start = { };
+			unsigned long loops = 0;
+			double err_busy, err_idle;
+			long get_time_d;
+
+			igt_nsec_elapsed(&test_start);
+			do {
+				struct timespec t_busy = { };
+
+				igt_nsec_elapsed(&t_busy);
+				__igt_spin_batch_restart(gem_fd, spin);
+				measured_usleep(sleep_busy);
+				igt_spin_batch_end(spin);
+				gem_sync(gem_fd, spin->handle);
+				busy_ns += igt_nsec_elapsed(&t_busy);
+
+				idle_ns += measured_usleep(sleep_idle);
+
+				loops++;
+			} while (igt_nsec_elapsed(&test_start) < timeout[pass]);
+
+			/* igt_nsec_elapsed overhead from measured_usleep. */
+			get_time_d = idle_ns - loops * sleep_idle * 1000;
+			busy_ns -= get_time_d;
+			busy_ns = div_round_up(busy_ns, loops);
+			idle_ns = div_round_up(idle_ns, loops);
+
+			err_busy = __error(busy_ns / 1000, busy_us);
+			err_idle = __error(idle_ns / 1000, idle_us);
+
+			igt_info("%u: busy %lu/%lu %.2f%%, idle %lu/%lu %.2f%%\n",
+				 pass,
+				 busy_ns / 1000, busy_us, err_busy,
+				 idle_ns / 1000, idle_us, err_idle);
+
+			if (pass == 0) {
+				sleep_busy = (double)busy_us -
+					     (double)busy_us * err_busy / 100.0;
+				sleep_idle = (double)idle_us -
+					     (double)idle_us * err_idle / 100.0;
+				igt_info("calibrated sleeps: busy=%lu, idle=%lu\n",
+					 sleep_busy, sleep_idle);
+			}
+		}
+
+		igt_spin_batch_free(gem_fd, spin);
+	}
+
+	/* Let the child run. */
+	usleep(pwm_calibration_us * 2);
+
+	/* Collect engine busyness for an interesting part of child runtime. */
+	fd = open_pmu(I915_PMU_ENGINE_BUSY(e->class, e->instance));
+	val[0] = __pmu_read_single(fd, &ts[0]);
+	usleep(test_us / 2);
+	val[1] = __pmu_read_single(fd, &ts[1]);
+	close(fd);
+
+	igt_waitchildren();
+
+	busy_r = (double)(val[1] - val[0]) / (ts[1] - ts[0]);
+
+	log_error("error", busy_r, target_busy_pct / 100.0);
+
+	assert_within_epsilon(busy_r, (double)target_busy_pct / 100.0, 0.15);
+}
+
 igt_main
 {
 	const unsigned int num_other_metrics =
@@ -1197,6 +1354,8 @@ igt_main
 		invalid_init();
 
 	for_each_engine_class_instance(fd, e) {
+		const unsigned int pct[] = { 2, 50, 98 };
+
 		/**
 		 * Test that a single engine metric can be initialized.
 		 */
@@ -1277,6 +1436,14 @@ igt_main
 		 */
 		igt_subtest_f("busy-double-start-%s", e->name)
 			busy_double_start(fd, e);
+
+		/**
+		 * Check engine busyness accuracy is as expected.
+		 */
+		for (i = 0; i < ARRAY_SIZE(pct); i++) {
+			igt_subtest_f("busy-accuracy-%u-%s", pct[i], e->name)
+				accuracy(fd, e, pct[i]);
+		}
 	}
 
 	/**
-- 
2.14.1

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