[Intel-gfx] [PATCH] drm/i915/pmu: Deprecate I915_PMU_LAST and optimize state tracking

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-11-26 16:47:03)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Adding any kinds of "last" abi markers is usually a mistake which I
> repeated when implementing the PMU because it felt convenient at the time.
> 
> This patch marks I915_PMU_LAST as deprecated and stops the internal
> implementation using it for sizing the event status bitmask and array.
> 
> New way of sizing the fields is a bit less elegant, but it omits reserving
> slots for tracking events we are not interested in, and as such saves some
> runtime space. Adding sampling events is likely to be a special event and
> the new plumbing needed will be easily detected in testing. Existing
> asserts against the bitfield and array sizes are keeping the code safe.
> 
> First event which gets the new treatment in this new scheme are the
> interrupts - which neither needs any tracking in i915 pmu nor needs
> waking up the GPU to read it.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_pmu.c | 64 +++++++++++++++++++++++++++------
>  drivers/gpu/drm/i915/i915_pmu.h | 35 ++++++++++++------
>  include/uapi/drm/i915_drm.h     |  2 +-
>  3 files changed, 78 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> index cd786ad12be7..cd564c709115 100644
> --- a/drivers/gpu/drm/i915/i915_pmu.c
> +++ b/drivers/gpu/drm/i915/i915_pmu.c
> @@ -27,8 +27,6 @@
>          BIT(I915_SAMPLE_WAIT) | \
>          BIT(I915_SAMPLE_SEMA))
>  
> -#define ENGINE_SAMPLE_BITS (1 << I915_PMU_SAMPLE_BITS)
> -
>  static cpumask_t i915_pmu_cpumask;
>  static unsigned int i915_pmu_target_cpu = -1;
>  
> @@ -57,12 +55,39 @@ static bool is_engine_config(u64 config)
>         return config < __I915_PMU_OTHER(0);
>  }
>  
> -static unsigned int config_enabled_bit(u64 config)
> +static unsigned int is_tracked_config(const u64 config)
>  {
> -       if (is_engine_config(config))
> +       unsigned int val;
> +
> +       switch (config) {
> +       case I915_PMU_ACTUAL_FREQUENCY:
> +               val =  __I915_PMU_ACTUAL_FREQUENCY_ENABLED;
> +               break;
> +       case I915_PMU_REQUESTED_FREQUENCY:
> +               val = __I915_PMU_REQUESTED_FREQUENCY_ENABLED;
> +               break;
> +       case I915_PMU_RC6_RESIDENCY:
> +               val = __I915_PMU_RC6_RESIDENCY_ENABLED;
> +               break;
> +       default:
> +               return 0;
> +       }
> +
> +       return val + 1;
> +}
> +
> +static unsigned int config_enabled_bit(const u64 config)
> +{
> +       if (is_engine_config(config)) {
>                 return engine_config_sample(config);
> -       else
> -               return ENGINE_SAMPLE_BITS + (config - __I915_PMU_OTHER(0));
> +       } else {
> +               unsigned int bit = is_tracked_config(config);
> +
> +               if (bit)
> +                       return I915_ENGINE_SAMPLE_COUNT + bit - 1;
> +               else
> +                       return -1;
> +       }
>  }
>  
>  static u64 config_enabled_mask(u64 config)
> @@ -80,10 +105,15 @@ static unsigned int event_enabled_bit(struct perf_event *event)
>         return config_enabled_bit(event->attr.config);
>  }
>  
> +static bool event_read_needs_wakeref(const struct perf_event *event)
> +{
> +       return event->attr.config == I915_PMU_RC6_RESIDENCY;
> +}
> +
>  static bool pmu_needs_timer(struct i915_pmu *pmu, bool gpu_active)
>  {
>         struct drm_i915_private *i915 = container_of(pmu, typeof(*i915), pmu);
> -       u64 enable;
> +       u32 enable;
>  
>         /*
>          * Only some counters need the sampling timer.
> @@ -627,12 +657,19 @@ static void i915_pmu_enable(struct perf_event *event)
>  {
>         struct drm_i915_private *i915 =
>                 container_of(event->pmu, typeof(*i915), pmu.base);
> -       unsigned int bit = event_enabled_bit(event);
> +       bool need_wakeref = event_read_needs_wakeref(event);
>         struct i915_pmu *pmu = &i915->pmu;
> -       intel_wakeref_t wakeref;
> +       intel_wakeref_t wakeref = 0;
>         unsigned long flags;
> +       unsigned int bit;
> +
> +       if (need_wakeref)
> +               wakeref = intel_runtime_pm_get(&i915->runtime_pm);
> +
> +       bit = event_enabled_bit(event);
> +       if (bit == -1)
> +               goto update;
>  
> -       wakeref = intel_runtime_pm_get(&i915->runtime_pm);
>         spin_lock_irqsave(&pmu->lock, flags);

What are we taking a wakeref here for?

Looks just to be __get_rc6. Do we need to update the sample at all?
-Chris