[Intel-gfx] [PATCH 7/7] drm/i915/perf: add flushing ioctl

[Joonas Lahtinen]

Quoting Lionel Landwerlin (2019-01-16 17:36:22)
> With the currently available parameters for the i915-perf stream,
> there are still situations that are not well covered :
> 
> If an application opens the stream with polling disable or at very low
> frequency and OA interrupt enabled, no data will be available even
> though somewhere between nothing and half of the OA buffer worth of
> data might have landed in memory.
> 
> To solve this issue we have a new flush ioctl on the perf stream that
> forces the i915-perf driver to look at the state of the buffer when
> called and makes any data available through both poll() & read() type
> syscalls.
> 
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>

Link to userspace changes?

Regards, Joonas

> ---
>  drivers/gpu/drm/i915/i915_perf.c | 17 +++++++++++++++++
>  include/uapi/drm/i915_drm.h      | 19 +++++++++++++++++++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> index da721fce2543..6c98ffa2135e 100644
> --- a/drivers/gpu/drm/i915/i915_perf.c
> +++ b/drivers/gpu/drm/i915/i915_perf.c
> @@ -2433,6 +2433,20 @@ static void i915_perf_disable_locked(struct i915_perf_stream *stream)
>                 stream->ops->disable(stream);
>  }
>  
> +/**
> + * i915_perf_flush_data - handle `I915_PERF_IOCTL_FLUSH_DATA` ioctl
> + * @stream: An enabled i915 perf stream
> + *
> + * The intention is to flush all the data available for reading from the OA
> + * buffer
> + */
> +static void i915_perf_flush_data(struct i915_perf_stream *stream)
> +{
> +       struct drm_i915_private *dev_priv = stream->dev_priv;
> +
> +       dev_priv->perf.oa.pollin = oa_buffer_check(stream->dev_priv, true);
> +}
> +
>  /**
>   * i915_perf_ioctl - support ioctl() usage with i915 perf stream FDs
>   * @stream: An i915 perf stream
> @@ -2456,6 +2470,9 @@ static long i915_perf_ioctl_locked(struct i915_perf_stream *stream,
>         case I915_PERF_IOCTL_DISABLE:
>                 i915_perf_disable_locked(stream);
>                 return 0;
> +       case I915_PERF_IOCTL_FLUSH_DATA:
> +               i915_perf_flush_data(stream);
> +               return 0;
>         }
>  
>         return -EINVAL;
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index b6db5e544a35..0f0d20080572 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -1594,6 +1594,25 @@ struct drm_i915_perf_open_param {
>   */
>  #define I915_PERF_IOCTL_DISABLE        _IO('i', 0x1)
>  
> +/**
> + * Actively check the availability of data from a stream.
> + *
> + * A stream data availability can be driven by two types of events :
> + *
> + *   - if enabled, the kernel's hrtimer checking the amount of available data
> + *     in the OA buffer through head/tail registers.
> + *
> + *   - if enabled, the OA unit's interrupt mechanism
> + *
> + * The kernel hrtimer incur a cost of running callback at fixed time
> + * intervals, while the OA interrupt might only happen rarely. In the
> + * situation where the application has disabled the kernel's hrtimer and only
> + * uses the OA interrupt to know about available data, the application can
> + * request an active check of the available OA data through this ioctl. This
> + * will make any data in the OA buffer available with either poll() or read().
> + */
> +#define I915_PERF_IOCTL_FLUSH_DATA _IO('i', 0x2)
> +
>  /**
>   * Common to all i915 perf records
>   */
> -- 
> 2.20.1
> 
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