[igt-dev] [PATCH i-g-t] i915/gem_exec_schedule: Measure timeslice distribution when oversaturated

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-12-15 09:41:09)
> 
> On 14/12/2020 20:44, Chris Wilson wrote:
> > Check that timeslices for an oversaturated system (where there is more
> > work than can be supported by a single engine) are evenly distributed
> > between the clients.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > ---
> >   tests/i915/gem_exec_schedule.c | 179 +++++++++++++++++++++++++++++++++
> >   1 file changed, 179 insertions(+)
> > 
> > diff --git a/tests/i915/gem_exec_schedule.c b/tests/i915/gem_exec_schedule.c
> > index f23d63ac3..263f1dd78 100644
> > --- a/tests/i915/gem_exec_schedule.c
> > +++ b/tests/i915/gem_exec_schedule.c
> > @@ -2516,6 +2516,154 @@ static void measure_semaphore_power(int i915)
> >       rapl_close(&pkg);
> >   }
> >   
> > +static int read_timestamp_frequency(int i915)
> > +{
> > +     int value = 0;
> > +     drm_i915_getparam_t gp = {
> > +             .value = &value,
> > +             .param = I915_PARAM_CS_TIMESTAMP_FREQUENCY,
> > +     };
> > +     ioctl(i915, DRM_IOCTL_I915_GETPARAM, &gp);
> > +     return value;
> > +}
> > +
> > +static uint64_t div64_u64_round_up(uint64_t x, uint64_t y)
> > +{
> > +     return (x + y - 1) / y;
> > +}
> > +
> > +static uint64_t ticks_to_ns(int i915, uint64_t ticks)
> > +{
> > +     return div64_u64_round_up(ticks * NSEC_PER_SEC,
> > +                               read_timestamp_frequency(i915));
> > +}
> > +
> > +static int cmp_u32(const void *A, const void *B)
> > +{
> > +     const uint32_t *a = A, *b = B;
> > +
> > +     if (*a < *b)
> > +             return -1;
> > +     else if (*a > *b)
> > +             return 1;
> > +     else
> > +             return 0;
> > +}
> > +
> > +static uint32_t read_ctx_timestamp(int i915,
> > +                                uint32_t ctx,
> > +                                const struct intel_execution_engine2 *e)
> > +{
> > +     const int use_64b = intel_gen(intel_get_drm_devid(i915)) >= 8;
> > +     const uint32_t base = gem_engine_mmio_base(i915, e->name);
> > +     struct drm_i915_gem_relocation_entry reloc;
> > +     struct drm_i915_gem_exec_object2 obj = {
> > +             .handle = gem_create(i915, 4096),
> > +             .offset = 32 << 20,
> > +             .relocs_ptr = to_user_pointer(&reloc),
> > +             .relocation_count = 1,
> > +     };
> > +     struct drm_i915_gem_execbuffer2 execbuf = {
> > +             .buffers_ptr = to_user_pointer(&obj),
> > +             .buffer_count = 1,
> > +             .flags = e->flags,
> > +             .rsvd1 = ctx,
> > +     };
> > +#define RUNTIME (base + 0x3a8)
> > +     uint32_t *map, *cs;
> > +     uint32_t ts;
> > +
> > +     igt_require(base);
> > +
> > +     cs = map = gem_mmap__device_coherent(i915, obj.handle,
> > +                                          0, 4096, PROT_WRITE);
> > +
> > +     *cs++ = 0x24 << 23 | (1 + use_64b); /* SRM */
> > +     *cs++ = RUNTIME;
> > +     memset(&reloc, 0, sizeof(reloc));
> > +     reloc.target_handle = obj.handle;
> > +     reloc.presumed_offset = obj.offset;
> > +     reloc.offset = offset_in_page(cs);
> > +     reloc.delta = 4000;
> > +     *cs++ = obj.offset + 4000;
> > +     *cs++ = obj.offset >> 32;
> > +
> > +     *cs++ = MI_BATCH_BUFFER_END;
> > +
> > +     gem_execbuf(i915, &execbuf);
> > +     gem_sync(i915, obj.handle);
> > +     gem_close(i915, obj.handle);
> > +
> > +     ts = map[1000];
> > +     munmap(map, 4096);
> > +
> > +     return ts;
> > +}
> > +
> > +static void fairslice(int i915,
> > +                   const struct intel_execution_engine2 *e,
> > +                   unsigned long flags,
> > +                   int duration)
> > +{
> > +     const double timeslice_duration_ns = 1e6;
> > +     igt_spin_t *spin = NULL;
> > +     double threshold;
> > +     uint32_t ctx[3];
> > +     uint32_t ts[3];
> > +
> > +     for (int i = 0; i < ARRAY_SIZE(ctx); i++) {
> > +             ctx[i] = gem_context_clone_with_engines(i915, 0);
> > +             if (spin == NULL) {
> > +                     spin = __igt_spin_new(i915,
> > +                                           .ctx = ctx[i],
> > +                                           .engine = e->flags,
> > +                                           .flags = flags);
> > +             } else {
> > +                     struct drm_i915_gem_execbuffer2 eb = {
> > +                             .buffer_count = 1,
> > +                             .buffers_ptr = to_user_pointer(&spin->obj[IGT_SPIN_BATCH]),
> > +                             .flags = e->flags,
> > +                             .rsvd1 = ctx[i],
> > +                     };
> > +                     gem_execbuf(i915, &eb);
> > +             }
> > +     }
> > +
> > +     sleep(duration); /* over the course of many timeslices */
> > +
> > +     igt_assert(gem_bo_busy(i915, spin->handle));
> > +     igt_spin_end(spin);
> > +     for (int i = 0; i < ARRAY_SIZE(ctx); i++)
> > +             ts[i] = read_ctx_timestamp(i915, ctx[i], e);
> > +
> > +     for (int i = 0; i < ARRAY_SIZE(ctx); i++)
> > +             gem_context_destroy(i915, ctx[i]);
> > +     igt_spin_free(i915, spin);
> > +
> > +     /*
> > +      * If we imagine that the timeslices are randomly distributed to
> > +      * the virtual engines, we would expect the variation to be modelled
> > +      * by a drunken walk; ergo sqrt(num_timeslices).
> > +      */
> > +     threshold = sqrt(1e9 * duration / timeslice_duration_ns);
> > +     threshold *= timeslice_duration_ns;
> > +     threshold *= 2; /* CI safety factor before crying wolf */
> > +
> > +     qsort(ts, 3, sizeof(*ts), cmp_u32);
> > +     igt_info("%s: [%.1f, %.1f, %.1f] ms, expect %1.f +- %.1fms\n", e->name,
> > +              1e-6 * ticks_to_ns(i915, ts[0]),
> > +              1e-6 * ticks_to_ns(i915, ts[1]),
> > +              1e-6 * ticks_to_ns(i915, ts[2]),
> > +              1e3 * duration / 3,
> > +              1e-6 * threshold);
> > +
> > +     igt_assert_f(ts[2], "CTX_TIMESTAMP not reported!\n");
> > +     igt_assert_f(ticks_to_ns(i915, ts[2] - ts[0]) < 2 * threshold,
> 
> Is this second threshold x2 by accident?

The drunken walk model's variance is evenly distributed about the mean
(one-sided). We are comparing max-min, so a two-sided range test.
-Chris