Re: [PATCH v6 2/7] drm/xe/uapi: Introduce API for EU stall sampling

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Tue, 17 Dec 2024 01:46:52 -0800, Harish Chegondi wrote:
>

Hi Harish,

Only reviewing the uapi once again.

> A user space consumer for this feature is Mesa.
>
> Mesa PR: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30142

Mesa PR should be in the cover letter, not in the patch itself. And we'll
need to eventually show that the Mesa PR is consuming all aspects of the
uapi being introduced.

>
> v6: Change the input sampling rate to GPU cycles instead of
>     GPU cycles multiplier.

Note that if your series is v6 each patch in the series is not necessarily
v6. A patch can be v2 e.g. So you should capture the version and changelog
of each patch separately.

> diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
> index f62689ca861a..4ee3b04a1bb5 100644
> --- a/include/uapi/drm/xe_drm.h
> +++ b/include/uapi/drm/xe_drm.h
> @@ -1397,6 +1397,8 @@ struct drm_xe_wait_user_fence {
>  enum drm_xe_observation_type {
>	/** @DRM_XE_OBSERVATION_TYPE_OA: OA observation stream type */
>	DRM_XE_OBSERVATION_TYPE_OA,
> +	/** @DRM_XE_OBSERVATION_TYPE_EU_STALL: EU stall sampling observation stream type */
> +	DRM_XE_OBSERVATION_TYPE_EU_STALL,
>  };
>
>  /**
> @@ -1729,6 +1731,45 @@ struct drm_xe_oa_stream_info {
>	__u64 reserved[3];
>  };
>
> +/**
> + * enum drm_xe_eu_stall_property_id - EU stall sampling input property ids.
> + *
> + * These properties are passed to the driver at open as a chain of
> + * @drm_xe_ext_set_property structures with @property set to these
> + * properties' enums and @value set to the corresponding values of these
> + * properties. @drm_xe_user_extension base.name should be set to
> + * @DRM_XE_EU_STALL_EXTENSION_SET_PROPERTY.
> + *
> + * With the file descriptor obtained from open, user space must enable
> + * the EU stall stream fd with @DRM_XE_OBSERVATION_IOCTL_ENABLE before
> + * calling read(). read() returns number of bytes of EU stall data read
> + * from the EU stall data buffer or an error. One of the errors returned

No need to explain what read() returns, read() is a system call, user can
read the read man page.

> + * from read is -EIO which indicates HW dropped data due to full buffer.

Just say "EIO errno from read() indicates data loss due to buffer
overflow".

Also, -EIO is not returned to userspace, errno is set for userspace.

> + *
> + */
> +enum drm_xe_eu_stall_property_id {
> +#define DRM_XE_EU_STALL_EXTENSION_SET_PROPERTY		0
> +	/**
> +	 * @DRM_XE_EU_STALL_PROP_GT_ID: GT ID of the GT on which

@gt_id

> +	 * EU stall data will be captured.
> +	 */
> +	DRM_XE_EU_STALL_PROP_GT_ID = 1,
> +
> +	/**
> +	 * @DRM_XE_EU_STALL_PROP_SAMPLE_RATE: Sampling rate
> +	 * in GPU cycles. Valid values are:
> +	 * 251, 251x2, 251x3, 251x4, 251x5, 251x6 and 251x7.

This 251 stuff needs to go, as was already mentioned the last
time. Something like:

"@DRM_XE_EU_STALL_PROP_SAMPLE_RATE: Sampling rate in GPU cycles, from
@sampling_rates in struct @drm_xe_query_eu_stall".

> +	 */
> +	DRM_XE_EU_STALL_PROP_SAMPLE_RATE,
> +
> +	/**
> +	 * @DRM_XE_EU_STALL_PROP_EVENT_REPORT_COUNT: Minimum number of
> +	 * EU stall data rows to be present in the kernel buffer for
> +	 * poll() to set POLLIN (data present).
> +	 */
> +	DRM_XE_EU_STALL_PROP_EVENT_REPORT_COUNT,

We called this DRM_XE_OA_PROPERTY_WAIT_NUM_REPORTS for OA. So maybe
DRM_XE_EU_STALL_PROP_WAIT_NUM_REPORTS? Or WAIT_REPORT_COUNT? Not sure what
EVENT is referring to?

> +};
> +
>  #if defined(__cplusplus)
>  }
>  #endif
> --
> 2.47.0
>

Ashutosh