[Intel-gfx] [RFC 1/4] drm/i915/perf: Add support to correlate GPU timestamp with system time

[Chris Wilson]

Quoting Sagar Arun Kamble (2017-11-15 12:13:51)
>  #include <drm/drmP.h>
>  #include <drm/intel-gtt.h>
> @@ -2149,6 +2150,14 @@ struct i915_perf_stream {
>          * @oa_config: The OA configuration used by the stream.
>          */
>         struct i915_oa_config *oa_config;
> +
> +       /**
> +        * System time correlation variables.
> +        */
> +       struct cyclecounter cc;
> +       spinlock_t systime_lock;
> +       struct timespec64 start_systime;
> +       struct timecounter tc;

This pattern is repeated a lot by struct timecounter users. (I'm still
trying to understand why the common case is not catered for by a
convenience timecounter api.)

>  };
>  
>  /**
> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> index 00be015..72ddc34 100644
> --- a/drivers/gpu/drm/i915/i915_perf.c
> +++ b/drivers/gpu/drm/i915/i915_perf.c
> @@ -192,6 +192,7 @@
>   */
>  
>  #include <linux/anon_inodes.h>
> +#include <linux/clocksource.h>
>  #include <linux/sizes.h>
>  #include <linux/uuid.h>
>  
> @@ -2391,6 +2392,56 @@ static unsigned int i915_perf_poll(struct file *file, poll_table *wait)
>  }
>  
>  /**
> + * i915_cyclecounter_read - read raw cycle/timestamp counter
> + * @cc: cyclecounter structure
> + */
> +static u64 i915_cyclecounter_read(const struct cyclecounter *cc)
> +{
> +       struct i915_perf_stream *stream = container_of(cc, typeof(*stream), cc);
> +       struct drm_i915_private *dev_priv = stream->dev_priv;
> +       u64 ts_count;
> +
> +       intel_runtime_pm_get(dev_priv);
> +       ts_count = I915_READ64_2x32(GEN4_TIMESTAMP,
> +                                   GEN7_TIMESTAMP_UDW);
> +       intel_runtime_pm_put(dev_priv);
> +
> +       return ts_count;
> +}
> +
> +static void i915_perf_init_cyclecounter(struct i915_perf_stream *stream)
> +{
> +       struct drm_i915_private *dev_priv = stream->dev_priv;
> +       int cs_ts_freq = dev_priv->perf.oa.timestamp_frequency;
> +       struct cyclecounter *cc = &stream->cc;
> +       u32 maxsec;
> +
> +       cc->read = i915_cyclecounter_read;
> +       cc->mask = CYCLECOUNTER_MASK(CS_TIMESTAMP_WIDTH(dev_priv));
> +       maxsec = cc->mask / cs_ts_freq;
> +
> +       clocks_calc_mult_shift(&cc->mult, &cc->shift, cs_ts_freq,
> +                              NSEC_PER_SEC, maxsec);
> +}
> +
> +static void i915_perf_init_timecounter(struct i915_perf_stream *stream)
> +{
> +#define SYSTIME_START_OFFSET   350000 /* Counter read takes about 350us */
> +       unsigned long flags;
> +       u64 ns;
> +
> +       i915_perf_init_cyclecounter(stream);
> +       spin_lock_init(&stream->systime_lock);
> +
> +       getnstimeofday64(&stream->start_systime);
> +       ns = timespec64_to_ns(&stream->start_systime) + SYSTIME_START_OFFSET;

Use ktime directly. Or else Arnd will be back with a patch to fix it.
(All non-ktime interfaces are effectively deprecated; obsolete for
drivers.)

> +       spin_lock_irqsave(&stream->systime_lock, flags);
> +       timecounter_init(&stream->tc, &stream->cc, ns);
> +       spin_unlock_irqrestore(&stream->systime_lock, flags);
> +}
> +
> +/**
>   * i915_perf_enable_locked - handle `I915_PERF_IOCTL_ENABLE` ioctl
>   * @stream: A disabled i915 perf stream
>   *
> @@ -2408,6 +2459,8 @@ static void i915_perf_enable_locked(struct i915_perf_stream *stream)
>         /* Allow stream->ops->enable() to refer to this */
>         stream->enabled = true;
>  
> +       i915_perf_init_timecounter(stream);
> +
>         if (stream->ops->enable)
>                 stream->ops->enable(stream);
>  }
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index cfdf4f8..e7e6966 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -8882,6 +8882,12 @@ enum skl_power_gate {
>  
>  /* Gen4+ Timestamp and Pipe Frame time stamp registers */
>  #define GEN4_TIMESTAMP         _MMIO(0x2358)
> +#define GEN7_TIMESTAMP_UDW     _MMIO(0x235C)
> +#define PRE_GEN7_TIMESTAMP_WIDTH       32
> +#define GEN7_TIMESTAMP_WIDTH           36
> +#define CS_TIMESTAMP_WIDTH(dev_priv) \
> +       (INTEL_GEN(dev_priv) < 7 ? PRE_GEN7_TIMESTAMP_WIDTH : \
> +                                  GEN7_TIMESTAMP_WIDTH)

s/PRE_GEN7/GEN4/ would be consistent.
If you really want to add support for earlier, I9XX_.

Ok. I can accept the justification, and we are not the only ones who do
the cyclecounter -> timecounter correction like this.
-Chris