drm/i915/selftests: Check power consumption at min/max frequencies

A basic premise of RPS is that at lower frequencies, not only do we run
slower, but we save power compared to higher frequencies. For example,
when idle, we set the minimum frequency just in case there is some
residual current. Since the power curve should be a physical
relationship, if we find no power saving it's likely that we've broken
our frequency handling, so test!
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Andi Shyti <andi.shyti@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200417152018.13079-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/selftest_gt_pm.c

@@ -54,6 +54,7 @@ int intel_gt_pm_live_selftests(struct drm_i915_private *i915)
 	static const struct i915_subtest tests[] = {
 		SUBTEST(live_rc6_manual),
 		SUBTEST(live_rps_interrupt),
+		SUBTEST(live_rps_power),
 		SUBTEST(live_gt_resume),
 	};
 

drivers/gpu/drm/i915/gt/selftest_rps.c

@@ -3,12 +3,15 @@
  * Copyright © 2020 Intel Corporation
  */
 
+#include <linux/sort.h>
+
 #include "intel_engine_pm.h"
 #include "intel_gt_pm.h"
 #include "intel_rc6.h"
 #include "selftest_rps.h"
 #include "selftests/igt_flush_test.h"
 #include "selftests/igt_spinner.h"
+#include "selftests/librapl.h"
 
 static void dummy_rps_work(struct work_struct *wrk)
 {
@@ -231,3 +234,138 @@ int live_rps_interrupt(void *arg)
 
 	return err;
 }
+
+static u64 __measure_power(int duration_ms)
+{
+	u64 dE, dt;
+
+	dt = ktime_get();
+	dE = librapl_energy_uJ();
+	usleep_range(1000 * duration_ms, 2000 * duration_ms);
+	dE = librapl_energy_uJ() - dE;
+	dt = ktime_get() - dt;
+
+	return div64_u64(1000 * 1000 * dE, dt);
+}
+
+static int cmp_u64(const void *A, const void *B)
+{
+	const u64 *a = A, *b = B;
+
+	if (a < b)
+		return -1;
+	else if (a > b)
+		return 1;
+	else
+		return 0;
+}
+
+static u64 measure_power_at(struct intel_rps *rps, int freq)
+{
+	u64 x[5];
+	int i;
+
+	mutex_lock(&rps->lock);
+	GEM_BUG_ON(!rps->active);
+	intel_rps_set(rps, freq);
+	mutex_unlock(&rps->lock);
+
+	msleep(20); /* more than enough time to stabilise! */
+
+	i = read_cagf(rps);
+	if (i != freq)
+		pr_notice("Running at %x [%uMHz], not target %x [%uMHz]\n",
+			  i, intel_gpu_freq(rps, i),
+			  freq, intel_gpu_freq(rps, freq));
+
+	for (i = 0; i < 5; i++)
+		x[i] = __measure_power(5);
+
+	/* A simple triangle filter for better result stability */
+	sort(x, 5, sizeof(*x), cmp_u64, NULL);
+	return div_u64(x[1] + 2 * x[2] + x[3], 4);
+}
+
+int live_rps_power(void *arg)
+{
+	struct intel_gt *gt = arg;
+	struct intel_rps *rps = &gt->rps;
+	void (*saved_work)(struct work_struct *wrk);
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
+	struct igt_spinner spin;
+	int err = 0;
+
+	/*
+	 * Our fundamental assumption is that running at lower frequency
+	 * actually saves power. Let's see if our RAPL measurement support
+	 * that theory.
+	 */
+
+	if (!rps->enabled || rps->max_freq <= rps->min_freq)
+		return 0;
+
+	if (!librapl_energy_uJ())
+		return 0;
+
+	if (igt_spinner_init(&spin, gt))
+		return -ENOMEM;
+
+	intel_gt_pm_wait_for_idle(gt);
+	saved_work = rps->work.func;
+	rps->work.func = dummy_rps_work;
+
+	for_each_engine(engine, gt, id) {
+		struct i915_request *rq;
+		u64 min, max;
+
+		if (!intel_engine_can_store_dword(engine))
+			continue;
+
+		rq = igt_spinner_create_request(&spin,
+						engine->kernel_context,
+						MI_NOOP);
+		if (IS_ERR(rq)) {
+			err = PTR_ERR(rq);
+			break;
+		}
+
+		i915_request_add(rq);
+
+		if (!igt_wait_for_spinner(&spin, rq)) {
+			pr_err("%s: RPS spinner did not start\n",
+			       engine->name);
+			intel_gt_set_wedged(engine->gt);
+			err = -EIO;
+			break;
+		}
+
+		max = measure_power_at(rps, rps->max_freq);
+		min = measure_power_at(rps, rps->min_freq);
+
+		igt_spinner_end(&spin);
+
+		pr_info("%s: min:%llumW @ %uMHz, max:%llumW @ %uMHz\n",
+			engine->name,
+			min, intel_gpu_freq(rps, rps->min_freq),
+			max, intel_gpu_freq(rps, rps->max_freq));
+		if (11 * min > 10 * max) {
+			pr_err("%s: did not conserve power when setting lower frequency!\n",
+			       engine->name);
+			err = -EINVAL;
+			break;
+		}
+
+		if (igt_flush_test(gt->i915)) {
+			err = -EIO;
+			break;
+		}
+	}
+
+	igt_spinner_fini(&spin);
+
+	intel_gt_pm_wait_for_idle(gt);
+	rps->work.func = saved_work;
+
+	return err;
+}

drivers/gpu/drm/i915/gt/selftest_rps.h

@@ -7,5 +7,6 @@
 #define SELFTEST_RPS_H
 
 int live_rps_interrupt(void *arg);
+int live_rps_power(void *arg);
 
 #endif /* SELFTEST_RPS_H */