Re: [PATCH i-g-t CI run 06/14] tests/intel/xe_oa: Rewrite the polling small buf test

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

On Mon, Feb 24, 2025 at 02:56:05PM -0800, Umesh Nerlige Ramappa wrote:
>On Mon, Feb 24, 2025 at 12:11:37PM -0800, Dixit, Ashutosh wrote:
>>On Tue, 18 Feb 2025 12:28:04 -0800, Umesh Nerlige Ramappa wrote:
>>>
>>
>>Hi Umesh,
>>
>>>Use mmio reads as a side-channel to determine if reports are available
>>>and ensure that poll will return with POLLIN set. Then provide a small
>>>buffer to force ENOSPC error. Then poll with a timeout of 0 to check if
>>>POLLIN is still set.
>>
>>Will need a reason for doing this here. But see below.
>>
>>>
>>>Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
>>>---
>>> tests/intel/xe_oa.c | 64 +++++++++++++++++++++++++--------------------
>>> 1 file changed, 35 insertions(+), 29 deletions(-)
>>>
>>>diff --git a/tests/intel/xe_oa.c b/tests/intel/xe_oa.c
>>>index aaf92308a..5792ffec2 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 +2225,57 @@ 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_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;
>>>+	int report_size = get_oa_format(default_test_set->perf_oa_format).size;
>>>+	u32 oa_tail, prev_tail;
>>>+	struct pollfd pollfd;
>>>+	uint8_t buf[10];
>>>+	int ret, i = 0;
>>>+
>>>+	intel_register_access_init(&mmio_data,
>>>+				   igt_device_get_pci_device(drm_fd), 0);
>>>
>>>	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;
>>>+#define OAG_OATAILPTR	(0xdb04)
>>>+	/* Save the current tail */
>>>+	prev_tail = oa_tail = intel_register_read(&mmio_data, OAG_OATAILPTR);
>>>
>>>-			ret = read(stream_fd, buf, sizeof(buf));
>>>-			if (ret >= 0)
>>>-				n_bytes_read += ret;
>>>-		}
>>>+	/* Kickstart the capture */
>>>+	do_ioctl(stream_fd, DRM_XE_OBSERVATION_IOCTL_ENABLE, 0);
>>>
>>>-		n_polls++;
>>>+	/* Wait for 5 reports */
>>
>>Wait for 5 reports or 10 ms ?
>>
>>
>>>+	while ((oa_tail - prev_tail) < (5 * report_size)) {
>>>+		usleep(1000);
>>>+		oa_tail = intel_register_read(&mmio_data, OAG_OATAILPTR);
>>>+		if (i++ > 10)
>>
>>So on slow platforms we might not get any reports in 10 ms? The idea here
>>should be to not have any timing dependence? So if we want to wait for 5
>>reports, just wait for 5 reports?

Oh, I think the loop was stuck while debugging something, so had added a 
counter to bail out in 10 iterations. I will remove that. We only need to 
wait for 5 reports.

>>
>>We tried doing this for the mmap OA buffer: see
>>mmap_wait_for_periodic_reports(), the function waits indefinitely.

You mean this:

while (num_periodic_reports < n) {
	usleep(4 * n * period_us);
	num_periodic_reports = 0;
	for (reports = (uint32_t *)oa_vaddr;
	     reports[0] && oa_timestamp(reports, fmt) && oa_report_is_periodic(reports);
	     reports += get_oa_format(fmt).size) {
		num_periodic_reports++;
	}
}

Well.. if your reports start coming in fast enough, then you would just spin 
in the inner for loop. Maybe break the inner for loop when 
num_periodic_reports >= n;

>>
>>So if this is done I am not sure if the intel_register_read() approach is
>>needed (but I didn't think of doing that :). But I guess we can use it to
>>see when there are N reports available.
>>
>>Longer term it would be nice to have a centralized function
>>wait_for_n_reports(int n) or something like that which different tests can
>>use.

Agree, except that some tests will read the actual reports, while others ust 
want to take a peek at how many reports are available without reading them. 
Since mmap is also a feature under test, I took the easier approach. We can 
always refine it if we find something better.
>
>>
>>>+			break;
>>>	}
>>>
>>>-	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);
>>>+	intel_register_access_fini(&mmio_data);
>>>
>>>-	__perf_close(stream_fd);
>>>+	/* Just read one report and expect ENOSPC */
>>>+	pollfd.fd = stream_fd;
>>>+	pollfd.events = POLLIN;
>>>+	poll(&pollfd, 1, 1000);
>>>+	igt_assert(pollfd.revents & POLLIN);
>>
>>Is the assumption here that the kernel timer is firing every 5 ms (so if
>>we've waited for 10 ms POLLIN must be set since the timer is firing every 5
>>ms)? I am not sure if that 5 ms is uapi. Or is it? Actually I was thinking

But here I am waiting 1000ms in the poll above. That should be sufficient 
for POLLIN  to be set. If not, we could set the timeout to a large value (a 
few seconds).

>>
>>>+	errno = 0;
>>>+	ret = read(stream_fd, buf, sizeof(buf));
>>>+	igt_assert_eq(ret, -1);
>>>+	igt_assert_eq(errno, ENOSPC);
>>
>>This part looks ok, it's uapi.
>>

Note:
ENOSPC is returned only if the buffer is small enough that not even one 
report will fit in. Initially I had a 600 byte buffer, but I did not get 
ENOSPC. Instead I got 576 in ret which I think is the correct behavior.

>>>
>>>-	igt_assert(abs(n_expect_read_bytes - n_bytes_read) <
>>>-		   0.20 * n_expect_read_bytes);
>>>+	/* Poll with 0 timeout and expect POLLIN flag to be set */
>>>+	poll(&pollfd, 1, 0);
>>>+	igt_assert(pollfd.revents & POLLIN);
>>>+
>>>+	__perf_close(stream_fd);
>>
>>How about just reading N reports using a small buffer for this test,
>>however long it takes? N can 5 or 10.

Not sure I understand. You mean at this stage of the test, read 5/10 
reports? OR just alter the entire test somehow to do something 
different?

I thought the test was specifically testing that POLLIN is still set 
after an ENOSPC error, so I have written it for that case alone. The 0 
timeout will bypass the wait in the poll so that we only get the state 
of POLLIN.

Thanks,
Umesh


>>
>>Thanks.
>>--
>>Ashutosh
>>
>>PS: how about separating out the patches which currently have R-b into a
>>separate series and merging them first?