[igt-dev] [PATCH i-g-t 2/3] tests/perf: new tests for OA interrupt

[Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>]

From: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

Those tests verify that the interrupt wakes up userspace waiting on
the perf stream either with poll() or with read().

v2: (Umesh)
  - If the fill_time is small enough then we will have 1 or 2 valid
    reports available before we even can call a read(). The blocking read()
    will check for reports in OA buffer prior to blocking for new
    reports. To enable the blocking with interrupt tests to work as expected,
    let the fill time be large so that the sampling rate is large enough
    for the blocking read to actually block.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

with '#' will be ignored, and an empty message aborts the commit.
---
 include/drm-uapi/i915_drm.h |  13 ++-
 tests/perf.c                | 210 ++++++++++++++++++++++++++++++++++++
 2 files changed, 222 insertions(+), 1 deletion(-)

diff --git a/include/drm-uapi/i915_drm.h b/include/drm-uapi/i915_drm.h
index 2b55af13..1b35952d 100644
--- a/include/drm-uapi/i915_drm.h
+++ b/include/drm-uapi/i915_drm.h
@@ -1987,12 +1987,23 @@ enum drm_i915_perf_property_id {
 	 * the driver if this parameter is not specified. Note that larger timer
 	 * values will reduce cpu consumption during OA perf captures. However,
 	 * excessively large values would potentially result in OA buffer
-	 * overwrites as captures reach end of the OA buffer.
+	 * overwrites as captures reach end of the OA buffer. A value of 0 means
+	 * no hrtimer will be started.
 	 *
 	 * This property is available in perf revision 5.
 	 */
 	DRM_I915_PERF_PROP_POLL_OA_PERIOD,
 
+	/**
+	 * Specifying this property sets up the interrupt mechanism for the OA
+	 * buffer in i915. This option in conjuction with a long polling period
+	 * for avaibility of OA data can reduce CPU load significantly if you
+	 * do not care about OA data being read as soon as it's available.
+	 *
+	 * This property is available in perf revision 6.
+	 */
+	DRM_I915_PERF_PROP_OA_ENABLE_INTERRUPT,
+
 	DRM_I915_PERF_PROP_MAX /* non-ABI */
 };
 
diff --git a/tests/perf.c b/tests/perf.c
index ca12090a..d9f5b2c0 100644
--- a/tests/perf.c
+++ b/tests/perf.c
@@ -450,6 +450,20 @@ oa_exponent_to_ns(int exponent)
        return 1000000000ULL * (2ULL << exponent) / intel_perf->devinfo.timestamp_frequency;
 }
 
+static int
+find_oa_exponent_for_buffer_fill_time(size_t oa_buf_size, size_t report_size, uint64_t fill_time_ns)
+{
+       size_t n_reports = oa_buf_size / report_size;
+
+       for (int e = 1; e < 32; e++) {
+               if (fill_time_ns < oa_exponent_to_ns(e) * n_reports)
+                       return e;
+       }
+
+       igt_assert(!"reached");
+       return -1;
+}
+
 static bool
 oa_report_is_periodic(uint32_t oa_exponent, const uint32_t *report)
 {
@@ -2434,6 +2448,111 @@ gen12_test_oa_tlb_invalidate(void)
 }
 
 
+static void
+test_interrupt(uint64_t oa_exponent,
+	       uint64_t kernel_oa_poll_delay,
+	       bool use_interrupt,
+	       bool expect_buffer_lost,
+	       bool use_polling,
+	       uint32_t expect_min_reports)
+{
+	uint64_t properties[] = {
+		/* Include OA reports in samples */
+		DRM_I915_PERF_PROP_SAMPLE_OA, true,
+
+		/* OA unit configuration */
+		DRM_I915_PERF_PROP_OA_METRICS_SET, test_set->perf_oa_metrics_set,
+		DRM_I915_PERF_PROP_OA_FORMAT, test_set->perf_oa_format,
+		DRM_I915_PERF_PROP_OA_EXPONENT, oa_exponent,
+		DRM_I915_PERF_PROP_OA_ENABLE_INTERRUPT, use_interrupt,
+
+		/* Kernel configuration */
+		DRM_I915_PERF_PROP_POLL_OA_PERIOD, kernel_oa_poll_delay,
+	};
+	struct drm_i915_perf_open_param param = {
+		.flags = I915_PERF_FLAG_FD_CLOEXEC |
+			I915_PERF_FLAG_DISABLED |
+			(use_polling ? I915_PERF_FLAG_FD_NONBLOCK : 0),
+		.num_properties = ARRAY_SIZE(properties) / 2,
+		.properties_ptr = to_user_pointer(properties),
+	};
+	struct pollfd pollfd = { .events = POLLIN };
+	struct drm_i915_perf_record_header *header;
+	uint32_t n_reports = 0;
+	bool buffer_lost = false;
+	uint8_t *buf = malloc(MAX_OA_BUF_SIZE);
+	int ret;
+
+	stream_fd = __perf_open(drm_fd, &param, true /* prevent_pm */);
+	pollfd.fd = stream_fd;
+
+	igt_debug("OA period = %s, ",
+		  pretty_print_oa_period(oa_exponent_to_ns(oa_exponent)));
+	igt_debug("OA poll delay = %s, use interrupt = %i, "
+		  "expected min report = %u\n",
+		  pretty_print_oa_period(kernel_oa_poll_delay),
+		  use_interrupt, expect_min_reports);
+
+	do_ioctl(stream_fd, I915_PERF_IOCTL_ENABLE, 0);
+
+	if (use_polling) {
+		while ((ret = poll(&pollfd, 1, -1)) < 0 &&
+		       errno == EINTR)
+			;
+		igt_assert_eq(ret, 1);
+		igt_assert(pollfd.revents & POLLIN);
+	}
+
+	while ((ret = read(stream_fd, buf, MAX_OA_BUF_SIZE)) < 0 &&
+	       errno == EINTR)
+		;
+
+	if (ret < 0)
+		igt_debug("Unexpected error when reading after poll = %d\n", errno);
+	igt_assert_neq(ret, -1);
+
+	__perf_close(stream_fd);
+
+	/* For Haswell reports don't contain a well defined reason
+	 * field we so assume all reports to be 'periodic'. For gen8+
+	 * we want to to consider that the HW automatically writes some
+	 * non periodic reports (e.g. on context switch) which might
+	 * lead to more successful read()s than expected due to
+	 * periodic sampling and we don't want these extra reads to
+	 * cause the test to fail...
+	 */
+	for (int offset = 0; offset < ret; offset += header->size) {
+		header = (void *)(buf + offset);
+
+		switch (header->type) {
+		case DRM_I915_PERF_RECORD_SAMPLE:
+			n_reports++;
+			break;
+		case DRM_I915_PERF_RECORD_OA_BUFFER_LOST:
+			buffer_lost = true;
+			break;
+		}
+	}
+
+	igt_debug("Got %i report(s)\n", n_reports);
+
+	igt_assert_eq(buffer_lost, expect_buffer_lost);
+
+	/*
+	 * Leave a 5% error margin for 2 reasons :
+	 *
+	 * - the tail pointer race condition might remove a couple of
+	 *   reports because things have not yet landed in memory.
+	 *
+	 * - the OA unit sometimes drop a writing a report here and
+	 *   there, the algorithm is linked to pressure on memory
+	 *   controller but undocumented.
+	 */
+	igt_assert_lte(expect_min_reports * 0.95, n_reports);
+
+	free(buf);
+}
+
 static void
 test_buffer_fill(void)
 {
@@ -4975,6 +5094,52 @@ igt_main
 			      5 * 1000 * 1000 /* default 2ms hrtimer */);
 	}
 
+	igt_describe("Test blocking read with interrupt and different hrtimer frequencies");
+	igt_subtest("blocking-with-interrupt") {
+		uint64_t target_fill_time = /* 5000ms */ 5000 * 1000 * 1000ul;
+		size_t report_size = get_oa_format(test_set->perf_oa_format).size;
+		uint32_t max_reports = MAX_OA_BUF_SIZE / report_size;
+		int oa_exponent =
+			find_oa_exponent_for_buffer_fill_time(MAX_OA_BUF_SIZE,
+							      report_size, target_fill_time);
+		uint64_t fill_time = oa_exponent_to_ns(oa_exponent) *
+			(MAX_OA_BUF_SIZE / report_size);
+
+		igt_require(i915_perf_revision(drm_fd) >= 6);
+
+		/*
+		 * We should be waken up by the HR timer but too late,
+		 * so we'll loose reports.
+		 */
+		test_interrupt(oa_exponent,
+			       fill_time + fill_time / 2,
+			       false /* interrupt */, true /* loss */, false /* use_polling */,
+			       0);
+
+		/*
+		 * We should get woken up by the HR timer and get the
+		 * appropriate number of report.
+		 */
+		test_interrupt(oa_exponent,
+			       /* 500us */ 500 * 1000,
+			       false /* interrupt */, false /* no loss */, false /* use_polling */,
+			       (500 * 1000 * max_reports) / fill_time);
+
+
+		/* We should be waken up by the interrupt first. */
+		test_interrupt(oa_exponent,
+			       2 * fill_time,
+			       true /* interrupt */, false /* no loss */, false /* use_polling */,
+			       max_reports / 2);
+
+		/* We should be waken up by the HR timer first. */
+		test_interrupt(oa_exponent,
+			       fill_time / 4,
+			       true /* interrupt */, false /* no loss */, false /* use_polling */,
+			       (fill_time / 4) * max_reports / fill_time);
+	}
+
+
 	igt_describe("Test polled read with default hrtimer frequency");
 	igt_subtest("polling") {
 		test_polling(40 * 1000 * 1000 /* 40ms oa period */,
@@ -4998,6 +5163,51 @@ igt_main
 	igt_subtest("polling-small-buf")
 		test_polling_small_buf();
 
+	igt_describe("Test polled read with interrupt and different hrtimer frequencies");
+	igt_subtest("polling-with-interrupt") {
+		uint64_t target_fill_time = /* 1000ms */ 1000 * 1000 * 1000ul;
+		size_t report_size = get_oa_format(test_set->perf_oa_format).size;
+		uint32_t max_reports = MAX_OA_BUF_SIZE / report_size;
+		int oa_exponent =
+			find_oa_exponent_for_buffer_fill_time(MAX_OA_BUF_SIZE,
+							      report_size, target_fill_time);
+		uint64_t fill_time = oa_exponent_to_ns(oa_exponent) *
+			(MAX_OA_BUF_SIZE / report_size);
+
+		igt_require(i915_perf_revision(drm_fd) >= 6);
+
+		/*
+		 * We should be waken up by the HR timer but too late,
+		 * so we'll loose reports.
+		 */
+		test_interrupt(oa_exponent,
+			       fill_time + fill_time / 2,
+			       false /* interrupt */, true /* loss */, true /* use_polling */,
+			       0);
+
+		/*
+		 * We should get woken up by the HR timer and get the
+		 * appropriate number of report.
+		 */
+		test_interrupt(oa_exponent,
+			       /* 500us */ 500 * 1000,
+			       false /* interrupt */, false /* no loss */, true /* use_polling */,
+			       (500 * 1000 * max_reports) / fill_time);
+
+
+		/* We should be waken up by the interrupt first. */
+		test_interrupt(oa_exponent,
+			       2 * fill_time,
+			       true /* interrupt */, false /* no loss */, true /* use_polling */,
+			       max_reports / 2);
+
+		/* We should be waken up by the HR timer first. */
+		test_interrupt(oa_exponent,
+			       fill_time / 4,
+			       true /* interrupt */, false /* no loss */, true /* use_polling */,
+			       (fill_time / 4) * max_reports / fill_time);
+	}
+
 	igt_subtest("short-reads")
 		test_short_reads();
 
-- 
2.20.1

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