Re: [Intel-gfx] [PATCH 7/7] drm/i915: Allow user to set cache at BO creation

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Mar 31, 2023 at 11:38:30PM -0700, fei.yang@intel.com wrote:
> From: Fei Yang <fei.yang@intel.com>
> 
> To comply with the design that buffer objects shall have immutable
> cache setting through out its life cycle, {set, get}_caching ioctl's
> are no longer supported from MTL onward. With that change caching
> policy can only be set at object creation time. The current code
> applies a default (platform dependent) cache setting for all objects.
> However this is not optimal for performance tuning. The patch extends
> the existing gem_create uAPI to let user set PAT index for the object
> at creation time.

This is missing the whole justification for the new uapi.
Why is MOCS not sufficient?

> The new extension is platform independent, so UMD's can switch to using
> this extension for older platforms as well, while {set, get}_caching are
> still supported on these legacy paltforms for compatibility reason.
> 
> Cc: Chris Wilson <chris.p.wilson@linux.intel.com>
> Cc: Matt Roper <matthew.d.roper@intel.com>
> Signed-off-by: Fei Yang <fei.yang@intel.com>
> Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_create.c | 33 ++++++++++++++++++++
>  include/uapi/drm/i915_drm.h                | 36 ++++++++++++++++++++++
>  tools/include/uapi/drm/i915_drm.h          | 36 ++++++++++++++++++++++
>  3 files changed, 105 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_create.c b/drivers/gpu/drm/i915/gem/i915_gem_create.c
> index e76c9703680e..1c6e2034d28e 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_create.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_create.c
> @@ -244,6 +244,7 @@ struct create_ext {
>  	unsigned int n_placements;
>  	unsigned int placement_mask;
>  	unsigned long flags;
> +	unsigned int pat_index;
>  };
>  
>  static void repr_placements(char *buf, size_t size,
> @@ -393,11 +394,39 @@ static int ext_set_protected(struct i915_user_extension __user *base, void *data
>  	return 0;
>  }
>  
> +static int ext_set_pat(struct i915_user_extension __user *base, void *data)
> +{
> +	struct create_ext *ext_data = data;
> +	struct drm_i915_private *i915 = ext_data->i915;
> +	struct drm_i915_gem_create_ext_set_pat ext;
> +	unsigned int max_pat_index;
> +
> +	BUILD_BUG_ON(sizeof(struct drm_i915_gem_create_ext_set_pat) !=
> +		     offsetofend(struct drm_i915_gem_create_ext_set_pat, rsvd));
> +
> +	if (copy_from_user(&ext, base, sizeof(ext)))
> +		return -EFAULT;
> +
> +	max_pat_index = INTEL_INFO(i915)->max_pat_index;
> +
> +	if (ext.pat_index > max_pat_index) {
> +		drm_dbg(&i915->drm, "PAT index is invalid: %u\n",
> +			ext.pat_index);
> +		return -EINVAL;
> +	}
> +
> +	ext_data->pat_index = ext.pat_index;
> +
> +	return 0;
> +}
> +
>  static const i915_user_extension_fn create_extensions[] = {
>  	[I915_GEM_CREATE_EXT_MEMORY_REGIONS] = ext_set_placements,
>  	[I915_GEM_CREATE_EXT_PROTECTED_CONTENT] = ext_set_protected,
> +	[I915_GEM_CREATE_EXT_SET_PAT] = ext_set_pat,
>  };
>  
> +#define PAT_INDEX_NOT_SET	0xffff
>  /**
>   * Creates a new mm object and returns a handle to it.
>   * @dev: drm device pointer
> @@ -417,6 +446,7 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data,
>  	if (args->flags & ~I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS)
>  		return -EINVAL;
>  
> +	ext_data.pat_index = PAT_INDEX_NOT_SET;
>  	ret = i915_user_extensions(u64_to_user_ptr(args->extensions),
>  				   create_extensions,
>  				   ARRAY_SIZE(create_extensions),
> @@ -453,5 +483,8 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data,
>  	if (IS_ERR(obj))
>  		return PTR_ERR(obj);
>  
> +	if (ext_data.pat_index != PAT_INDEX_NOT_SET)
> +		i915_gem_object_set_pat_index(obj, ext_data.pat_index);
> +
>  	return i915_gem_publish(obj, file, &args->size, &args->handle);
>  }
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index dba7c5a5b25e..03c5c314846e 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -3630,9 +3630,13 @@ struct drm_i915_gem_create_ext {
>  	 *
>  	 * For I915_GEM_CREATE_EXT_PROTECTED_CONTENT usage see
>  	 * struct drm_i915_gem_create_ext_protected_content.
> +	 *
> +	 * For I915_GEM_CREATE_EXT_SET_PAT usage see
> +	 * struct drm_i915_gem_create_ext_set_pat.
>  	 */
>  #define I915_GEM_CREATE_EXT_MEMORY_REGIONS 0
>  #define I915_GEM_CREATE_EXT_PROTECTED_CONTENT 1
> +#define I915_GEM_CREATE_EXT_SET_PAT 2
>  	__u64 extensions;
>  };
>  
> @@ -3747,6 +3751,38 @@ struct drm_i915_gem_create_ext_protected_content {
>  	__u32 flags;
>  };
>  
> +/**
> + * struct drm_i915_gem_create_ext_set_pat - The
> + * I915_GEM_CREATE_EXT_SET_PAT extension.
> + *
> + * If this extension is provided, the specified caching policy (PAT index) is
> + * applied to the buffer object.
> + *
> + * Below is an example on how to create an object with specific caching policy:
> + *
> + * .. code-block:: C
> + *
> + *      struct drm_i915_gem_create_ext_set_pat set_pat_ext = {
> + *              .base = { .name = I915_GEM_CREATE_EXT_SET_PAT },
> + *              .pat_index = 0,
> + *      };
> + *      struct drm_i915_gem_create_ext create_ext = {
> + *              .size = PAGE_SIZE,
> + *              .extensions = (uintptr_t)&set_pat_ext,
> + *      };
> + *
> + *      int err = ioctl(fd, DRM_IOCTL_I915_GEM_CREATE_EXT, &create_ext);
> + *      if (err) ...
> + */
> +struct drm_i915_gem_create_ext_set_pat {
> +	/** @base: Extension link. See struct i915_user_extension. */
> +	struct i915_user_extension base;
> +	/** @pat_index: PAT index to be set */
> +	__u32 pat_index;
> +	/** @rsvd: reserved for future use */
> +	__u32 rsvd;
> +};
> +
>  /* ID of the protected content session managed by i915 when PXP is active */
>  #define I915_PROTECTED_CONTENT_DEFAULT_SESSION 0xf
>  
> diff --git a/tools/include/uapi/drm/i915_drm.h b/tools/include/uapi/drm/i915_drm.h
> index 8df261c5ab9b..8cdcdb5fac26 100644
> --- a/tools/include/uapi/drm/i915_drm.h
> +++ b/tools/include/uapi/drm/i915_drm.h
> @@ -3607,9 +3607,13 @@ struct drm_i915_gem_create_ext {
>  	 *
>  	 * For I915_GEM_CREATE_EXT_PROTECTED_CONTENT usage see
>  	 * struct drm_i915_gem_create_ext_protected_content.
> +	 *
> +	 * For I915_GEM_CREATE_EXT_SET_PAT usage see
> +	 * struct drm_i915_gem_create_ext_set_pat.
>  	 */
>  #define I915_GEM_CREATE_EXT_MEMORY_REGIONS 0
>  #define I915_GEM_CREATE_EXT_PROTECTED_CONTENT 1
> +#define I915_GEM_CREATE_EXT_SET_PAT 2
>  	__u64 extensions;
>  };
>  
> @@ -3724,6 +3728,38 @@ struct drm_i915_gem_create_ext_protected_content {
>  	__u32 flags;
>  };
>  
> +/**
> + * struct drm_i915_gem_create_ext_set_pat - The
> + * I915_GEM_CREATE_EXT_SET_PAT extension.
> + *
> + * If this extension is provided, the specified caching policy (PAT index) is
> + * applied to the buffer object.
> + *
> + * Below is an example on how to create an object with specific caching policy:
> + *
> + * .. code-block:: C
> + *
> + *      struct drm_i915_gem_create_ext_set_pat set_pat_ext = {
> + *              .base = { .name = I915_GEM_CREATE_EXT_SET_PAT },
> + *              .pat_index = 0,
> + *      };
> + *      struct drm_i915_gem_create_ext create_ext = {
> + *              .size = PAGE_SIZE,
> + *              .extensions = (uintptr_t)&set_pat_ext,
> + *      };
> + *
> + *      int err = ioctl(fd, DRM_IOCTL_I915_GEM_CREATE_EXT, &create_ext);
> + *      if (err) ...
> + */
> +struct drm_i915_gem_create_ext_set_pat {
> +	/** @base: Extension link. See struct i915_user_extension. */
> +	struct i915_user_extension base;
> +	/** @pat_index: PAT index to be set */
> +	__u32 pat_index;
> +	/** @rsvd: reserved for future use */
> +	__u32 rsvd;
> +};
> +
>  /* ID of the protected content session managed by i915 when PXP is active */
>  #define I915_PROTECTED_CONTENT_DEFAULT_SESSION 0xf
>  
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel