Re: [PATCH 08/25] drm/i915/pmu: Always sample an active ringbuffer

Mika Kuoppala
2019-02-22T12:31:51Z

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Quoting Mika Kuoppala (2019-02-22 12:10:33)
>> Chris Wilson <chris@chris-wilson.co.uk> writes:
>>
>> > As we no longer have a precise indication of requests queued to an
>> > engine, make no presumptions and just sample the ring registers to see
>> > if the engine is busy.
>> >
>> > v2: Report busy while the ring is idling on a semaphore/event.
>> > v3: Give the struct a name!
>> > v4: Always 0 outside the powerwell; trusting the powerwell is
>> > accurate enough for our sampling pmu.
>> >
>> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>> > ---
>> > drivers/gpu/drm/i915/i915_pmu.c | 60 ++++++++++---------------
>> > drivers/gpu/drm/i915/intel_ringbuffer.h | 2 +-
>> > 2 files changed, 24 insertions(+), 38 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
>> > index 13d70b90dd0f..21adad72bd86 100644
>> > --- a/drivers/gpu/drm/i915/i915_pmu.c
>> > +++ b/drivers/gpu/drm/i915/i915_pmu.c
>> > @@ -148,14 +148,6 @@ void i915_pmu_gt_unparked(struct drm_i915_private *i915)
>> > spin_unlock_irq(&i915->pmu.lock);
>> > }
>> >
>> > -static bool grab_forcewake(struct drm_i915_private *i915, bool fw)
>> > -{
>> > - if (!fw)
>> > - intel_uncore_forcewake_get(i915, FORCEWAKE_ALL);
>> > -
>> > - return true;
>> > -}
>> > -
>> > static void
>> > add_sample(struct i915_pmu_sample *sample, u32 val)
>> > {
>> > @@ -168,49 +160,43 @@ engines_sample(struct drm_i915_private *dev_priv, unsigned int period_ns)
>> > struct intel_engine_cs *engine;
>> > enum intel_engine_id id;
>> > intel_wakeref_t wakeref;
>> > - bool fw = false;
>> >
>> > if ((dev_priv->pmu.enable & ENGINE_SAMPLE_MASK) == 0)
>> > return;
>> >
>> > - if (!dev_priv->gt.awake)
>> > - return;
>> > -
>> > - wakeref = intel_runtime_pm_get_if_in_use(dev_priv);
>> > + wakeref = 0;
>> > + if (READ_ONCE(dev_priv->gt.awake))
>>
>> Is this gt.awake check just to be more lightweight on sampling?
>
> Yes, we know that if !awake, then we are idle and are done with
> sampling. It also ties in later with a patch to change how we handle rpm
> suspend periods (which is why I went with writing it in this idiom).
>
>> > + wakeref = intel_runtime_pm_get_if_in_use(dev_priv);
>> > if (!wakeref)
>> > return;
>> >
>> > for_each_engine(engine, dev_priv, id) {
>> > - u32 current_seqno = intel_engine_get_seqno(engine);
>> > - u32 last_seqno = intel_engine_last_submit(engine);
>> > + struct intel_engine_pmu *pmu = &engine->pmu;
>> > + bool busy;
>> > u32 val;
>> >
>> > - val = !i915_seqno_passed(current_seqno, last_seqno);
>> > -
>> > - if (val)
>> > - add_sample(&engine->pmu.sample[I915_SAMPLE_BUSY],
>> > - period_ns);
>> > -
>> > - if (val && (engine->pmu.enable &
>> > - (BIT(I915_SAMPLE_WAIT) | BIT(I915_SAMPLE_SEMA)))) {
>> > - fw = grab_forcewake(dev_priv, fw);
>> > -
>> > - val = I915_READ_FW(RING_CTL(engine->mmio_base));
>> > - } else {
>> > - val = 0;
>> > - }
>> > + val = I915_READ_FW(RING_CTL(engine->mmio_base));
>> > + if (val == 0) /* powerwell off => engine idle */
>> > + continue;
>> >
>> > if (val & RING_WAIT)
>> > - add_sample(&engine->pmu.sample[I915_SAMPLE_WAIT],
>> > - period_ns);
>> > -
>> > + add_sample(&pmu->sample[I915_SAMPLE_WAIT], period_ns);
>> > if (val & RING_WAIT_SEMAPHORE)
>> > - add_sample(&engine->pmu.sample[I915_SAMPLE_SEMA],
>> > - period_ns);
>> > - }
>> > + add_sample(&pmu->sample[I915_SAMPLE_SEMA], period_ns);
>> >
>> > - if (fw)
>> > - intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
>> > + /*
>> > + * MI_MODE reports IDLE if the ring is waiting, but we regard
>> > + * this as being busy instead, as the engine is busy with the
>> > + * user request.
>> > + */
>> > + busy = val & (RING_WAIT_SEMAPHORE | RING_WAIT);
>> > + if (!busy) {
>> > + val = I915_READ_FW(RING_MI_MODE(engine->mmio_base));
>> > + busy = !(val & MODE_IDLE);
>>
>> The comment makes sense if you do
>> busy = val & MODE_IDLE;
>
> /*
> * While waiting on a semaphore or event, MI_MODE reports the ring as
> * idle. However, previously using the seqno, and with execlists sampling,
> * we account for the ring waiting as the engine being busy. Therefore,
> * we record the sample as being busy if either waiting or !idle.
> */

Altho now the original makes more sense too, I like this one better!

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>