Quoting Tvrtko Ursulin (2018-08-09 12:54:41)
>
> On 08/08/2018 15:59, Chris Wilson wrote:
> > Our observation is that the systematic error is proportional to the
> > number of iterations we perform; the suspicion is that it directly
> > correlates with the number of sleeps. Reduce the number of iterations,
> > to try and keep the error in check.
> >
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> > ---
> > tests/perf_pmu.c | 34 +++++++++++++++++++++-------------
> > 1 file changed, 21 insertions(+), 13 deletions(-)
> >
> > diff --git a/tests/perf_pmu.c b/tests/perf_pmu.c
> > index 9a20abb6b..5a26d5272 100644
> > --- a/tests/perf_pmu.c
> > +++ b/tests/perf_pmu.c
> > @@ -1521,14 +1521,13 @@ static void __rearm_spin_batch(igt_spin_t *spin)
> >
> > static void
> > accuracy(int gem_fd, const struct intel_execution_engine2 *e,
> > - unsigned long target_busy_pct)
> > + unsigned long target_busy_pct,
> > + unsigned long target_iters)
> > {
> > - unsigned long busy_us = 10000 - 100 * (1 + abs(50 - target_busy_pct));
> > - unsigned long idle_us = 100 * (busy_us - target_busy_pct *
> > - busy_us / 100) / target_busy_pct;
> > const unsigned long min_test_us = 1e6;
> > - const unsigned long pwm_calibration_us = min_test_us;
> > - const unsigned long test_us = min_test_us;
> > + unsigned long pwm_calibration_us;
> > + unsigned long test_us;
> > + unsigned long cycle_us, busy_us, idle_us;
> > double busy_r, expected;
> > uint64_t val[2];
> > uint64_t ts[2];
> > @@ -1538,18 +1537,27 @@ accuracy(int gem_fd, const struct intel_execution_engine2 *e,
> > /* Sampling platforms cannot reach the high accuracy criteria. */
> > igt_require(gem_has_execlists(gem_fd));
> >
> > - while (idle_us < 2500) {
> > + /* Aim for approximately 100 iterations for calibration */
> > + cycle_us = min_test_us / target_iters;
> > + busy_us = cycle_us * target_busy_pct / 100;
> > + idle_us = cycle_us - busy_us;
>
> 2% load, 1s / 10 iters
> cycles_us = 100ms
> busy_us = 2ms
> idle_us = 98ms
> ...
>
> > +
> > + while (idle_us < 2500 || busy_us < 2500) {
> > busy_us *= 2;
> > idle_us *= 2;
>
> ...
>
> busy_us = 4ms
> idle_us = 196ms
Currently it is 250ms per 98:2 cycle and about 20ms per 50:50 cycle. So
we are only doing 4 and 50 iterations respectively.
10 cycles is strictly an improvement :-p
-Chris
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