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

[Lionel Landwerlin]

On 26/03/2020 07:42, Ashutosh Dixit wrote:
> 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.


There seems to be a fundamental issue with this test, it's supposed to 
test a broken behavior with revision < 5 but then avoid testing anything 
there ;)


I've modified this test a bit here : 
https://gitlab.freedesktop.org/llandwerlin/igt-gpu-tools/-/tree/for-ashutosh

It's failing stable kernels.


Increasing the size of the buffer to 1Mb make the test pass.


-Lionel


>
> Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
> Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> Signed-off--by: Ashutosh Dixit <ashutosh.dixit at intel.com>
> ---
>   tests/perf.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 81 insertions(+)
>
> diff --git a/tests/perf.c b/tests/perf.c
> index 724f6f809..41e3b4478 100644
> --- a/tests/perf.c
> +++ b/tests/perf.c
> @@ -2265,6 +2265,81 @@ test_polling(void)
>   	__perf_close(stream_fd);
>   }
>   
> +static void test_polling_small_buf(void)
> +{
> +	int oa_exponent = max_oa_exponent_for_period_lte(10 * 1000 * 1000); /* 10ms */
> +	/* Use a large value for the timer for a large amout of data to accumulate */
> +	uint64_t kernel_hrtimer = 400 * 1000 * 1000; /* 400 ms */
> +	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,
> +
> +		/* Kernel configuration (optional) */
> +		DRM_I915_PERF_PROP_POLL_OA_PERIOD, kernel_hrtimer,
> +	};
> +	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),
> +	};
> +	uint8_t buf[1024 * 1024];
> +	int ret, iterl = 0, iters = 0, large = 0, small = 0;
> +	struct timespec tsl = {}, tss = {};
> +
> +	stream_fd = __perf_open(drm_fd, &param, true /* prevent_pm */);
> +	do_ioctl(stream_fd, I915_PERF_IOCTL_ENABLE, 0);
> +
> +	/* First do non blocking reads for 4 seconds using 1 MB buffer */
> +	igt_nsec_elapsed(&tsl);
> +	igt_until_timeout(4) {
> +		struct pollfd pollfd = { .fd = stream_fd, .events = POLLIN };
> +
> +		ret = poll(&pollfd, 1, -1);
> +		igt_assert_eq(ret, 1);
> +		igt_assert(pollfd.revents & POLLIN);
> +
> +		ret = read(stream_fd, buf, sizeof(buf));
> +		igt_assert(ret > 0);
> +		large += ret;
> +		iterl++;
> +	}
> +	igt_debug("Read %d B in %d iterations in %ld ns using 1 MB buffer\n",
> +		  large, iterl, igt_nsec_elapsed(&tsl));
> +
> +	/* Now repeat the read with a 4 KB buffer */
> +	igt_nsec_elapsed(&tss);
> +	igt_until_timeout(4) {
> +		struct pollfd pollfd = { .fd = stream_fd, .events = POLLIN };
> +
> +		ret = poll(&pollfd, 1, -1);
> +		igt_assert_eq(ret, 1);
> +		igt_assert(pollfd.revents & POLLIN);
> +
> +		ret = read(stream_fd, buf, 4096);
> +		igt_assert(ret > 0);
> +		small += ret;
> +		iters++;
> +	}
> +	igt_debug("Read %d B in %d iterations in %ld ns using 4 KB buffer\n",
> +		  small, iters, igt_nsec_elapsed(&tss));
> +
> +	__perf_close(stream_fd);
> +
> +	/* Check that data read using the two methods is within 20% of each
> +	 * other. Differences between the two cases is due to timing coupled
> +	 * with granularity of the data reads, but they are still expected to be
> +	 * "close".
> +	 */
> +	igt_assert(abs(large - small) * 100 / ((large + small) / 2) < 20);
> +}
> +
>   static int
>   num_valid_reports_captured(struct drm_i915_perf_open_param *param,
>   			   int64_t *duration_ns)
> @@ -4676,6 +4751,12 @@ igt_main
>   	igt_subtest("polling")
>   		test_polling();
>   
> +	igt_describe("Test polled read with buffer size smaller than available data");
> +	igt_subtest("polling-small-buf") {
> +		igt_require(i915_perf_revision(drm_fd) >= 5);
> +		test_polling_small_buf();
> +	}
> +
>   	igt_subtest("short-reads")
>   		test_short_reads();
>