Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> Repeat the measurement of the clock frequency a few times and use the
> median to try and reduce the systematic measurement error.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gt/selftest_rps.c | 54 +++++++++++++++++++-------
> 1 file changed, 40 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/selftest_rps.c b/drivers/gpu/drm/i915/gt/selftest_rps.c
> index b89a7d7611f6..bfa1a15564f7 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_rps.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_rps.c
> @@ -56,6 +56,18 @@ static int cmp_u64(const void *A, const void *B)
> return 0;
> }
>
> +static int cmp_u32(const void *A, const void *B)
> +{
> + const u32 *a = A, *b = B;
> +
> + if (a < b)
> + return -1;
> + else if (a > b)
> + return 1;
> + else
> + return 0;
> +}
> +
> static struct i915_vma *
> create_spin_counter(struct intel_engine_cs *engine,
> struct i915_address_space *vm,
> @@ -236,8 +248,8 @@ int live_rps_clock_interval(void *arg)
> for_each_engine(engine, gt, id) {
> unsigned long saved_heartbeat;
> struct i915_request *rq;
> - ktime_t dt;
> u32 cycles;
> + u64 dt;
>
> if (!intel_engine_can_store_dword(engine))
> continue;
> @@ -286,15 +298,29 @@ int live_rps_clock_interval(void *arg)
> engine->name);
> err = -ENODEV;
> } else {
> - preempt_disable();
> - dt = ktime_get();
> - cycles = -intel_uncore_read_fw(gt->uncore,
> - GEN6_RP_CUR_UP_EI);
> - udelay(1000);
> - dt = ktime_sub(ktime_get(), dt);
> - cycles += intel_uncore_read_fw(gt->uncore,
> - GEN6_RP_CUR_UP_EI);
> - preempt_enable();
> + ktime_t dt_[5];
> + u32 cycles_[5];
> + int i;
> +
> + for (i = 0; i < 5; i++) {
Could be sizeof.
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> + preempt_disable();
> +
> + dt_[i] = ktime_get();
> + cycles_[i] = -intel_uncore_read_fw(gt->uncore, GEN6_RP_CUR_UP_EI);
> +
> + udelay(1000);
> +
> + dt_[i] = ktime_sub(ktime_get(), dt_[i]);
> + cycles_[i] += intel_uncore_read_fw(gt->uncore, GEN6_RP_CUR_UP_EI);
> +
> + preempt_enable();
> + }
> +
> + /* Use the median of both cycle/dt; close enough */
> + sort(cycles_, 5, sizeof(*cycles_), cmp_u32, NULL);
> + cycles = (cycles_[1] + 2 * cycles_[2] + cycles_[3]) / 4;
> + sort(dt_, 5, sizeof(*dt_), cmp_u64, NULL);
> + dt = div_u64(dt_[1] + 2 * dt_[2] + dt_[3], 4);
> }
>
> intel_uncore_write_fw(gt->uncore, GEN6_RP_CONTROL, 0);
> @@ -306,14 +332,14 @@ int live_rps_clock_interval(void *arg)
> if (err == 0) {
> u64 time = intel_gt_pm_interval_to_ns(gt, cycles);
> u32 expected =
> - intel_gt_ns_to_pm_interval(gt, ktime_to_ns(dt));
> + intel_gt_ns_to_pm_interval(gt, dt);
>
> pr_info("%s: rps counted %d C0 cycles [%lldns] in %lldns [%d cycles], using GT clock frequency of %uKHz\n",
> - engine->name, cycles, time, ktime_to_ns(dt), expected,
> + engine->name, cycles, time, dt, expected,
> gt->clock_frequency / 1000);
>
> - if (10 * time < 8 * ktime_to_ns(dt) ||
> - 8 * time > 10 * ktime_to_ns(dt)) {
> + if (10 * time < 8 * dt ||
> + 8 * time > 10 * dt) {
> pr_err("%s: rps clock time does not match walltime!\n",
> engine->name);
> err = -EINVAL;
> --
> 2.20.1
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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