[Intel-gfx] [RFC i-g-t] tests/perf_pmu: Verify engine busyness accuracy

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-12-12 14:53:00)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> A subtest to verify that the engine busyness is reported with expected
> accuracy on platforms where the feature is available.
> 
> We test three patterns: 2%, 50% and 98% load per engine.
> 
> Problematic part is we also rely on scheduling latencies and the no-op
> batch calibration accuracy. For these reasons we use a large-ish tolerance
> and also set the load emitting process to SCHED_FIFO.
> 
> Load calibration is also moved to a subtest group fixture so the set-up
> time is shared between all subtests which use it.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>  tests/perf_pmu.c | 125 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 115 insertions(+), 10 deletions(-)
> 
> diff --git a/tests/perf_pmu.c b/tests/perf_pmu.c
> index db7696115a7b..ec6b0ee1cb86 100644
> --- a/tests/perf_pmu.c
> +++ b/tests/perf_pmu.c
> @@ -35,6 +35,7 @@
>  #include <dirent.h>
>  #include <time.h>
>  #include <poll.h>
> +#include <sched.h>
>  
>  #include "igt.h"
>  #include "igt_core.h"
> @@ -79,6 +80,17 @@ init(int gem_fd, const struct intel_execution_engine2 *e, uint8_t sample)
>         close(fd);
>  }
>  
> +static uint64_t __pmu_read_single(int fd, uint64_t *ts)
> +{
> +       uint64_t data[2];
> +
> +       igt_assert_eq(read(fd, data, sizeof(data)), sizeof(data));
> +
> +       *ts = data[1];
> +
> +       return data[0];
> +}
> +
>  static uint64_t pmu_read_single(int fd)
>  {
>         uint64_t data[2];
> @@ -665,6 +677,77 @@ multi_client(int gem_fd, const struct intel_execution_engine2 *e)
>         assert_within_epsilon(val[1], slept, tolerance);
>  }
>  
> +static void
> +accuracy(int gem_fd, const struct intel_execution_engine2 *e,
> +        unsigned long cal_ms_sz, unsigned long target_busy_pct)
> +{
> +       const unsigned long busy_us = 2500;
> +       const unsigned long idle_us = 100 * (busy_us - target_busy_pct *
> +                                     busy_us / 100) / target_busy_pct;
> +       const unsigned int test_us = 1e6;
> +       double busy_r;
> +       uint64_t val[2];
> +       uint64_t ts[2];
> +       int fd;
> +
> +       igt_require(intel_gen(intel_get_drm_devid(gem_fd)) >= 8);
> +
> +       assert_within_epsilon((double)busy_us / (busy_us + idle_us),
> +                             (double)target_busy_pct / 100.0, tolerance);
> +
> +       /* Emit PWM pattern on the engine from a child. */
> +       igt_fork(child, 1) {
> +               struct sched_param rt = { .sched_priority = 99 };
> +               const uint32_t bbe = MI_BATCH_BUFFER_END;
> +               const unsigned long loops = test_us / (busy_us + idle_us);
> +               const unsigned long sz = ALIGN(busy_us * cal_ms_sz / 1000,
> +                                              sizeof(uint32_t));
> +               struct drm_i915_gem_exec_object2 obj = { };
> +               struct drm_i915_gem_execbuffer2 eb = {
> +                               .buffers_ptr = to_user_pointer(&obj),
> +                               .buffer_count = 1,
> +                               .flags = e2ring(gem_fd, e)
> +                       };
> +               unsigned long i;
> +
> +               /* We need the best sleep accuracy we can get. */
> +               igt_require(sched_setscheduler(0,
> +                                              SCHED_FIFO | SCHED_RESET_ON_FORK,
> +                                              &rt) == 0);
> +
> +               obj.handle = gem_create(gem_fd, sz);
> +               gem_write(gem_fd, obj.handle, sz - sizeof(bbe), &bbe,
> +                         sizeof(bbe));
> +
> +               for (i = 0; i < loops; i++) {
> +                       gem_execbuf(gem_fd, &eb);
> +                       gem_sync(gem_fd, obj.handle);
> +                       usleep(idle_us);
> +               }
> +
> +               gem_close(gem_fd, obj.handle);
> +       }

Wouldn't using a signaling thread and a igt_spin_t give you better
accuracy, with the bonus of not requiring calibration?
-Chris