[igt-dev] [PATCH i-g-t] tests/perf: add a test for OA data polling reads using "small" buffers

[Ashutosh Dixit]

Add a test for OA data non-blocking reads using buffers smaller than
the available data. This test would fail for perf revisions < 5
because poll would block even when data was available. Therefore the
amount of data read was limited by the buffer size and the timer
interval and it was impossible to read all available data. This issue
is fixed in perf revision 5.

v2: Complete rewrite, make test fail on existing kernels (Lionel)

Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
---
 tests/perf.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/tests/perf.c b/tests/perf.c
index 724f6f809..3dc757c3b 100644
--- a/tests/perf.c
+++ b/tests/perf.c
@@ -2265,6 +2265,71 @@ test_polling(void)
 	__perf_close(stream_fd);
 }
 
+static void test_polling_small_buf(void)
+{
+	int oa_exponent = max_oa_exponent_for_period_lte(40 * 1000); /* 40us */
+	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,
+	};
+	struct drm_i915_perf_open_param param = {
+		.flags = I915_PERF_FLAG_FD_CLOEXEC |
+			I915_PERF_FLAG_DISABLED |
+			I915_PERF_FLAG_FD_NONBLOCK,
+		.num_properties = NUM_PROPERTIES(properties),
+		.properties_ptr = to_user_pointer(properties),
+	};
+	uint32_t test_duration = 80 * 1000 * 1000;
+	int sample_size = (sizeof(struct drm_i915_perf_record_header) +
+				get_oa_format(test_set->perf_oa_format).size);
+	int n_expected_reports = test_duration / oa_exponent_to_ns(oa_exponent);
+	int n_expect_read_bytes = n_expected_reports * sample_size;
+	uint8_t buf[1024];
+	int n_bytes_read = 0;
+	uint32_t n_polls = 0;
+	struct timespec ts = {};
+
+	stream_fd = __perf_open(drm_fd, &param, true /* prevent_pm */);
+	do_ioctl(stream_fd, I915_PERF_IOCTL_ENABLE, 0);
+
+	igt_nsec_elapsed(&ts);
+
+	while (igt_nsec_elapsed(&ts) < test_duration) {
+		struct timespec poll_wait = {
+			.tv_sec = 0,
+			.tv_nsec = (test_duration - igt_nsec_elapsed(&ts)),
+		};
+		struct pollfd pollfd = { .fd = stream_fd, .events = POLLIN };
+		int ret;
+
+		ret = ppoll(&pollfd, 1, &poll_wait, NULL);
+
+		if (pollfd.revents & POLLIN) {
+			ret = read(stream_fd, buf, sizeof(buf));
+			if (ret >= 0)
+				n_bytes_read += ret;
+		}
+
+		n_polls++;
+
+		igt_debug("Elapsed=%lu wait=%lu\n", igt_nsec_elapsed(&ts), poll_wait.tv_nsec);
+	}
+
+	igt_info("Read %d expected %d (%.2f%% of the expected number), polls=%u\n",
+		  n_bytes_read, n_expect_read_bytes,
+		  n_bytes_read * 100.0f / n_expect_read_bytes,
+		  n_polls);
+
+	__perf_close(stream_fd);
+
+	igt_assert(abs(n_expect_read_bytes - n_bytes_read) < (0.10 * n_expect_read_bytes));
+}
+
 static int
 num_valid_reports_captured(struct drm_i915_perf_open_param *param,
 			   int64_t *duration_ns)
@@ -4676,6 +4741,10 @@ igt_main
 	igt_subtest("polling")
 		test_polling();
 
+	igt_describe("Test polled read with buffer size smaller than available data");
+	igt_subtest("polling-small-buf")
+		test_polling_small_buf();
+
 	igt_subtest("short-reads")
 		test_short_reads();
 
-- 
2.25.2