[igt-dev] [i-g-t] Fixing the latency of hrtimer

[Lionel Landwerlin]

On 27/08/2020 15:02, Sowmya Kaparthi wrote:
> This test undergoes sanity check that we are not spending more than
> 1/100th of the time awake in the kernel. The right thing would be to
> adjust that value by the number of expected wakeups. We expect the
> kernel time not to exceed 1/100th of the total test duration at the
> default hrtimer of 200Hz/every5ms. Scale that by the provided hrtimer if
> applicable.
>
> Cc: Landwerlin, Lionel G <lionel.g.landwerlin at intel.com>
> Signed-off-by: Sowmya Kaparthi <sowmyax.kaparthi at intel.com>
> ---
>   tests/i915/perf.c | 16 ++++++++++++++--
>   1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/tests/i915/perf.c b/tests/i915/perf.c
> index a894fd38..952da84c 100644
> --- a/tests/i915/perf.c
> +++ b/tests/i915/perf.c
> @@ -1993,6 +1993,7 @@ test_blocking(uint64_t requested_oa_period, bool set_kernel_hrtimer, uint64_t ke
>   
>   	int64_t start, end;
>   	int n = 0;
> +	uint64_t max_expected_kernel_ns;
>   
>   	stream_fd = __perf_open(drm_fd, &param, true /* prevent_pm */);
>   
> @@ -2098,7 +2099,12 @@ test_blocking(uint64_t requested_oa_period, bool set_kernel_hrtimer, uint64_t ke
>   	 */
>   	igt_assert(n > (min_iterations + n_extra_iterations));
>   
> -	igt_assert(kernel_ns <= (test_duration_ns / 100ull));
> +	if (set_kernel_hrtimer)
> +		max_expected_kernel_ns = kernel_hrtimer * (test_duration_ns / 100);

That's not quite right.


test_duration_ns / 100 is the expectation for a 5ms kernel_hrtimer.

You can't just multiply that by kernel_hrtimer, it has a be proportional.


Thanks,


-Lionel


> +	else
> +		max_expected_kernel_ns = test_duration_ns / 100;
> +
> +	igt_assert(kernel_ns <= max_expected_kernel_ns);
>   
>   	__perf_close(stream_fd);
>   }
> @@ -2152,6 +2158,7 @@ test_polling(uint64_t requested_oa_period, bool set_kernel_hrtimer, uint64_t ker
>   	int min_iterations = (test_duration_ns / (oa_period + (kernel_hrtimer + kernel_hrtimer / 5)));
>   	int64_t start, end;
>   	int n = 0;
> +	uint64_t max_expected_kernel_ns;
>   
>   	stream_fd = __perf_open(drm_fd, &param, true /* prevent_pm */);
>   
> @@ -2286,7 +2293,12 @@ test_polling(uint64_t requested_oa_period, bool set_kernel_hrtimer, uint64_t ker
>   	 */
>   	igt_assert(n > (min_iterations + n_extra_iterations));
>   
> -	igt_assert(kernel_ns <= (test_duration_ns / 100ull));
> +	if (set_kernel_hrtimer)
> +		max_expected_kernel_ns = kernel_hrtimer * (test_duration_ns / 100);
> +	else
> +		max_expected_kernel_ns = test_duration_ns / 100;
> +
> +	igt_assert(kernel_ns <= max_expected_kernel_ns);
>   
>   	__perf_close(stream_fd);
>   }