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@xxxxxxxxx>
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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