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

[Umesh Nerlige Ramappa]

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 at 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 
just 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
>of changing that 5 ms time or changing the timer to a delayed work.

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?