[PATCH i-g-t v2 07/14] tests/intel/xe_oa: Rewrite the polling small buf test

[Umesh Nerlige Ramappa]

The polling-small-buf test is specifically testing that POLLIN is still
set after an ENOSPC error. In the buggy code, POLLIN was cleared on
the ENOSPC error even though there was data to be read. The test was
putting an upper bound on the number of bytes read in a fixed duration
of time. While this worked, we had occassional failures that were due to
scheduling and other dependencies outside the scope of this test.

In an attempt to make the test more robust,
- use a more definitive method to wait for few reports
- force an ENOSPC error using a small buffer
- Ensure POLLIN is still set in the subsequent poll() call

v2:
- Add "why" in commit message (Ashutosh)
- Use uapi to wait for N reports

Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
---
 tests/intel/xe_oa.c | 53 ++++++++++++++++++++-------------------------
 1 file changed, 23 insertions(+), 30 deletions(-)

diff --git a/tests/intel/xe_oa.c b/tests/intel/xe_oa.c
index 08406ca5c..dd16b39a9 100644
--- a/tests/intel/xe_oa.c
+++ b/tests/intel/xe_oa.c
@@ -2216,7 +2216,6 @@ static void test_polling(uint64_t requested_oa_period,
  */
 static void test_polling_small_buf(void)
 {
-	int oa_exponent = max_oa_exponent_for_period_lte(40 * 1000); /* 40us */
 	uint64_t properties[] = {
 		DRM_XE_OA_PROPERTY_OA_UNIT_ID, 0,
 
@@ -2226,50 +2225,44 @@ static void test_polling_small_buf(void)
 		/* OA unit configuration */
 		DRM_XE_OA_PROPERTY_OA_METRIC_SET, default_test_set->perf_oa_metrics_set,
 		DRM_XE_OA_PROPERTY_OA_FORMAT, __ff(default_test_set->perf_oa_format),
-		DRM_XE_OA_PROPERTY_OA_PERIOD_EXPONENT, oa_exponent,
+		DRM_XE_OA_PROPERTY_OA_PERIOD_EXPONENT, oa_exponent_default,
+		DRM_XE_OA_PROPERTY_WAIT_NUM_REPORTS, 5,
 		DRM_XE_OA_PROPERTY_OA_DISABLED, true,
 	};
 	struct intel_xe_oa_open_prop param = {
 		.num_properties = ARRAY_SIZE(properties) / 2,
 		.properties_ptr = to_user_pointer(properties),
 	};
-	uint32_t test_duration = 80 * 1000 * 1000;
-	int sample_size = get_oa_format(default_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;
-	struct timespec ts = {};
-	int n_bytes_read = 0;
-	uint32_t n_polls = 0;
+	struct pollfd pollfd;
+	uint8_t buf[10];
+	int ret;
 
 	stream_fd = __perf_open(drm_fd, &param, true /* prevent_pm */);
 	set_fd_flags(stream_fd, O_CLOEXEC | O_NONBLOCK);
-	do_ioctl(stream_fd, DRM_XE_OBSERVATION_IOCTL_ENABLE, 0);
 
-	while (igt_nsec_elapsed(&ts) < test_duration) {
-		struct pollfd pollfd = { .fd = stream_fd, .events = POLLIN };
-
-		ppoll(&pollfd, 1, NULL, NULL);
-		if (pollfd.revents & POLLIN) {
-			uint8_t buf[1024];
-			int ret;
+	/* Kickstart the capture */
+	do_ioctl(stream_fd, DRM_XE_OBSERVATION_IOCTL_ENABLE, 0);
 
-			ret = read(stream_fd, buf, sizeof(buf));
-			if (ret >= 0)
-				n_bytes_read += ret;
-		}
+	/*
+	 * Wait for number of reports specified in
+	 * DRM_XE_OA_PROPERTY_WAIT_NUM_REPORTS
+	 */
+	pollfd.fd = stream_fd;
+	pollfd.events = POLLIN;
+	poll(&pollfd, 1, -1);
+	igt_assert(pollfd.revents & POLLIN);
 
-		n_polls++;
-	}
+	/* Just read one report and expect ENOSPC */
+	errno = 0;
+	ret = read(stream_fd, buf, sizeof(buf));
+	igt_assert_eq(ret, -1);
+	igt_assert_eq(errno, ENOSPC);
 
-	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);
+	/* Poll with 0 timeout and expect POLLIN flag to be set */
+	poll(&pollfd, 1, 0);
+	igt_assert(pollfd.revents & POLLIN);
 
 	__perf_close(stream_fd);
-
-	igt_assert(abs(n_expect_read_bytes - n_bytes_read) <
-		   0.20 * n_expect_read_bytes);
 }
 
 static int
-- 
2.34.1