Re: [PATCH 06/13] tests/intel/xe_oa: Rewrite the polling small buf test

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

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?

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

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.

> +			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.

> +	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.

>
> -	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.

Thanks.
--
Ashutosh