On Tue, Feb 06, 2018 at 04:04:10PM +0000, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2018-02-06 14:31:07)
> > +static u64 read_rc6_residency(struct drm_i915_private *i915)
> > +{
> > + u64 val;
> > +
> > + val = intel_rc6_residency_ns(i915, IS_VALLEYVIEW(i915) ?
> > + VLV_GT_RENDER_RC6 : GEN6_GT_GFX_RC6);
> > + if (HAS_RC6p(i915))
> > + val += intel_rc6_residency_ns(i915, GEN6_GT_GFX_RC6p);
> > + if (HAS_RC6pp(i915))
> > + val += intel_rc6_residency_ns(i915, GEN6_GT_GFX_RC6pp);
>
> We really should mention that these may produce interesting results
> every 53 minutes. Switching to a timer will allow us to notice the
> wraparound in each counter.
>
> > +
> > + return val;
> > +}
> > +
> > +static void
> > +update_rc6_sample(struct drm_i915_private *i915, u64 val, bool locked)
> > +{
> > + unsigned long flags;
> > +
> > + if (!locked)
> > + spin_lock_irqsave(&i915->pmu.lock, flags);
> > +
> > + /*
> > + * Update stored RC6 counter only if it is greater than the current
> > + * value. This deals with periods of runtime suspend during which we are
> > + * estimating the RC6 residency, so do not want to overshoot the real
> > + * value read once the device is woken up.
> > + */
> > + if (val > i915->pmu.sample[__I915_SAMPLE_RC6].cur)
> > + i915->pmu.sample[__I915_SAMPLE_RC6].cur = val;
>
> 64b wraparound? Maybe not today, maybe not tomorrow... ;)
>
> > +
> > + /* We don't need to sample RC6 from the timer any more. */
> > + i915->pmu.timer_enabled =
> > + __pmu_needs_timer(i915,
> > + i915->pmu.enable & ~config_enabled_mask(I915_PMU_RC6_RESIDENCY),
> > + READ_ONCE(i915->gt.awake));
>
> But we do... :)
> One thing I had in mind was to hook into runtime suspend/resume to read
> the counters there and compensate, but the more I think about it, we may
> as well solve the lack of resolution in the rc6 counters whilst we are
> here. https://bugs.freedesktop.org/show_bug.cgi?id=94852.
How about using dev->power.suspended_jiffies?
--Imre
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