[PATCH v2 01/12] drm/doc: add rfc section for small BAR uapi
Lionel Landwerlin
lionel.g.landwerlin at intel.com
Tue Jun 21 18:31:39 UTC 2022
On 21/06/2022 13:44, Matthew Auld wrote:
> Add an entry for the new uapi needed for small BAR on DG2+.
>
> v2:
> - Some spelling fixes and other small tweaks. (Akeem & Thomas)
> - Rework error capture interactions, including no longer needing
> NEEDS_CPU_ACCESS for objects marked for capture. (Thomas)
> - Add probed_cpu_visible_size. (Lionel)
> v3:
> - Drop the vma query for now.
> - Add unallocated_cpu_visible_size as part of the region query.
> - Improve the docs some more, including documenting the expected
> behaviour on older kernels, since this came up in some offline
> discussion.
> v4:
> - Various improvements all over. (Tvrtko)
>
> v5:
> - Include newer integrated platforms when applying the non-recoverable
> context and error capture restriction. (Thomas)
>
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> Cc: Jon Bloomfield <jon.bloomfield at intel.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Kenneth Graunke <kenneth at whitecape.org>
> Cc: Akeem G Abodunrin <akeem.g.abodunrin at intel.com>
> Cc: mesa-dev at lists.freedesktop.org
> Acked-by: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> Acked-by: Akeem G Abodunrin <akeem.g.abodunrin at intel.com>
With Jordan with have changes for Anv/Iris :
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16739
Acked-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> ---
> Documentation/gpu/rfc/i915_small_bar.h | 189 +++++++++++++++++++++++
> Documentation/gpu/rfc/i915_small_bar.rst | 47 ++++++
> Documentation/gpu/rfc/index.rst | 4 +
> 3 files changed, 240 insertions(+)
> create mode 100644 Documentation/gpu/rfc/i915_small_bar.h
> create mode 100644 Documentation/gpu/rfc/i915_small_bar.rst
>
> diff --git a/Documentation/gpu/rfc/i915_small_bar.h b/Documentation/gpu/rfc/i915_small_bar.h
> new file mode 100644
> index 000000000000..752bb2ceb399
> --- /dev/null
> +++ b/Documentation/gpu/rfc/i915_small_bar.h
> @@ -0,0 +1,189 @@
> +/**
> + * struct __drm_i915_memory_region_info - Describes one region as known to the
> + * driver.
> + *
> + * Note this is using both struct drm_i915_query_item and struct drm_i915_query.
> + * For this new query we are adding the new query id DRM_I915_QUERY_MEMORY_REGIONS
> + * at &drm_i915_query_item.query_id.
> + */
> +struct __drm_i915_memory_region_info {
> + /** @region: The class:instance pair encoding */
> + struct drm_i915_gem_memory_class_instance region;
> +
> + /** @rsvd0: MBZ */
> + __u32 rsvd0;
> +
> + /**
> + * @probed_size: Memory probed by the driver (-1 = unknown)
> + *
> + * Note that it should not be possible to ever encounter a zero value
> + * here, also note that no current region type will ever return -1 here.
> + * Although for future region types, this might be a possibility. The
> + * same applies to the other size fields.
> + */
> + __u64 probed_size;
> +
> + /**
> + * @unallocated_size: Estimate of memory remaining (-1 = unknown)
> + *
> + * Requires CAP_PERFMON or CAP_SYS_ADMIN to get reliable accounting.
> + * Without this (or if this is an older kernel) the value here will
> + * always equal the @probed_size. Note this is only currently tracked
> + * for I915_MEMORY_CLASS_DEVICE regions (for other types the value here
> + * will always equal the @probed_size).
> + */
> + __u64 unallocated_size;
> +
> + union {
> + /** @rsvd1: MBZ */
> + __u64 rsvd1[8];
> + struct {
> + /**
> + * @probed_cpu_visible_size: Memory probed by the driver
> + * that is CPU accessible. (-1 = unknown).
> + *
> + * This will be always be <= @probed_size, and the
> + * remainder (if there is any) will not be CPU
> + * accessible.
> + *
> + * On systems without small BAR, the @probed_size will
> + * always equal the @probed_cpu_visible_size, since all
> + * of it will be CPU accessible.
> + *
> + * Note this is only tracked for
> + * I915_MEMORY_CLASS_DEVICE regions (for other types the
> + * value here will always equal the @probed_size).
> + *
> + * Note that if the value returned here is zero, then
> + * this must be an old kernel which lacks the relevant
> + * small-bar uAPI support (including
> + * I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS), but on
> + * such systems we should never actually end up with a
> + * small BAR configuration, assuming we are able to load
> + * the kernel module. Hence it should be safe to treat
> + * this the same as when @probed_cpu_visible_size ==
> + * @probed_size.
> + */
> + __u64 probed_cpu_visible_size;
> +
> + /**
> + * @unallocated_cpu_visible_size: Estimate of CPU
> + * visible memory remaining (-1 = unknown).
> + *
> + * Note this is only tracked for
> + * I915_MEMORY_CLASS_DEVICE regions (for other types the
> + * value here will always equal the
> + * @probed_cpu_visible_size).
> + *
> + * Requires CAP_PERFMON or CAP_SYS_ADMIN to get reliable
> + * accounting. Without this the value here will always
> + * equal the @probed_cpu_visible_size. Note this is only
> + * currently tracked for I915_MEMORY_CLASS_DEVICE
> + * regions (for other types the value here will also
> + * always equal the @probed_cpu_visible_size).
> + *
> + * If this is an older kernel the value here will be
> + * zero, see also @probed_cpu_visible_size.
> + */
> + __u64 unallocated_cpu_visible_size;
> + };
> + };
> +};
> +
> +/**
> + * struct __drm_i915_gem_create_ext - Existing gem_create behaviour, with added
> + * extension support using struct i915_user_extension.
> + *
> + * Note that new buffer flags should be added here, at least for the stuff that
> + * is immutable. Previously we would have two ioctls, one to create the object
> + * with gem_create, and another to apply various parameters, however this
> + * creates some ambiguity for the params which are considered immutable. Also in
> + * general we're phasing out the various SET/GET ioctls.
> + */
> +struct __drm_i915_gem_create_ext {
> + /**
> + * @size: Requested size for the object.
> + *
> + * The (page-aligned) allocated size for the object will be returned.
> + *
> + * Note that for some devices we have might have further minimum
> + * page-size restrictions (larger than 4K), like for device local-memory.
> + * However in general the final size here should always reflect any
> + * rounding up, if for example using the I915_GEM_CREATE_EXT_MEMORY_REGIONS
> + * extension to place the object in device local-memory. The kernel will
> + * always select the largest minimum page-size for the set of possible
> + * placements as the value to use when rounding up the @size.
> + */
> + __u64 size;
> +
> + /**
> + * @handle: Returned handle for the object.
> + *
> + * Object handles are nonzero.
> + */
> + __u32 handle;
> +
> + /**
> + * @flags: Optional flags.
> + *
> + * Supported values:
> + *
> + * I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS - Signal to the kernel that
> + * the object will need to be accessed via the CPU.
> + *
> + * Only valid when placing objects in I915_MEMORY_CLASS_DEVICE, and only
> + * strictly required on configurations where some subset of the device
> + * memory is directly visible/mappable through the CPU (which we also
> + * call small BAR), like on some DG2+ systems. Note that this is quite
> + * undesirable, but due to various factors like the client CPU, BIOS etc
> + * it's something we can expect to see in the wild. See
> + * &__drm_i915_memory_region_info.probed_cpu_visible_size for how to
> + * determine if this system applies.
> + *
> + * Note that one of the placements MUST be I915_MEMORY_CLASS_SYSTEM, to
> + * ensure the kernel can always spill the allocation to system memory,
> + * if the object can't be allocated in the mappable part of
> + * I915_MEMORY_CLASS_DEVICE.
> + *
> + * Also note that since the kernel only supports flat-CCS on objects
> + * that can *only* be placed in I915_MEMORY_CLASS_DEVICE, we therefore
> + * don't support I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS together with
> + * flat-CCS.
> + *
> + * Without this hint, the kernel will assume that non-mappable
> + * I915_MEMORY_CLASS_DEVICE is preferred for this object. Note that the
> + * kernel can still migrate the object to the mappable part, as a last
> + * resort, if userspace ever CPU faults this object, but this might be
> + * expensive, and so ideally should be avoided.
> + *
> + * On older kernels which lack the relevant small-bar uAPI support (see
> + * also &__drm_i915_memory_region_info.probed_cpu_visible_size),
> + * usage of the flag will result in an error, but it should NEVER be
> + * possible to end up with a small BAR configuration, assuming we can
> + * also successfully load the i915 kernel module. In such cases the
> + * entire I915_MEMORY_CLASS_DEVICE region will be CPU accessible, and as
> + * such there are zero restrictions on where the object can be placed.
> + */
> +#define I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS (1 << 0)
> + __u32 flags;
> +
> + /**
> + * @extensions: The chain of extensions to apply to this object.
> + *
> + * This will be useful in the future when we need to support several
> + * different extensions, and we need to apply more than one when
> + * creating the object. See struct i915_user_extension.
> + *
> + * If we don't supply any extensions then we get the same old gem_create
> + * behaviour.
> + *
> + * For I915_GEM_CREATE_EXT_MEMORY_REGIONS usage see
> + * struct drm_i915_gem_create_ext_memory_regions.
> + *
> + * For I915_GEM_CREATE_EXT_PROTECTED_CONTENT usage see
> + * struct drm_i915_gem_create_ext_protected_content.
> + */
> +#define I915_GEM_CREATE_EXT_MEMORY_REGIONS 0
> +#define I915_GEM_CREATE_EXT_PROTECTED_CONTENT 1
> + __u64 extensions;
> +};
> diff --git a/Documentation/gpu/rfc/i915_small_bar.rst b/Documentation/gpu/rfc/i915_small_bar.rst
> new file mode 100644
> index 000000000000..d6c03ce3b862
> --- /dev/null
> +++ b/Documentation/gpu/rfc/i915_small_bar.rst
> @@ -0,0 +1,47 @@
> +==========================
> +I915 Small BAR RFC Section
> +==========================
> +Starting from DG2 we will have resizable BAR support for device local-memory(i.e
> +I915_MEMORY_CLASS_DEVICE), but in some cases the final BAR size might still be
> +smaller than the total probed_size. In such cases, only some subset of
> +I915_MEMORY_CLASS_DEVICE will be CPU accessible(for example the first 256M),
> +while the remainder is only accessible via the GPU.
> +
> +I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS flag
> +----------------------------------------------
> +New gem_create_ext flag to tell the kernel that a BO will require CPU access.
> +This becomes important when placing an object in I915_MEMORY_CLASS_DEVICE, where
> +underneath the device has a small BAR, meaning only some portion of it is CPU
> +accessible. Without this flag the kernel will assume that CPU access is not
> +required, and prioritize using the non-CPU visible portion of
> +I915_MEMORY_CLASS_DEVICE.
> +
> +.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h
> + :functions: __drm_i915_gem_create_ext
> +
> +probed_cpu_visible_size attribute
> +---------------------------------
> +New struct__drm_i915_memory_region attribute which returns the total size of the
> +CPU accessible portion, for the particular region. This should only be
> +applicable for I915_MEMORY_CLASS_DEVICE. We also report the
> +unallocated_cpu_visible_size, alongside the unallocated_size.
> +
> +Vulkan will need this as part of creating a separate VkMemoryHeap with the
> +VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT set, to represent the CPU visible portion,
> +where the total size of the heap needs to be known. It also wants to be able to
> +give a rough estimate of how memory can potentially be allocated.
> +
> +.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h
> + :functions: __drm_i915_memory_region_info
> +
> +Error Capture restrictions
> +--------------------------
> +With error capture we have two new restrictions:
> +
> + 1) Error capture is best effort on small BAR systems; if the pages are not
> + CPU accessible, at the time of capture, then the kernel is free to skip
> + trying to capture them.
> +
> + 2) On discrete and newer integrated platforms we now reject error capture
> + on recoverable contexts. In the future the kernel may want to blit during
> + error capture, when for example something is not currently CPU accessible.
> diff --git a/Documentation/gpu/rfc/index.rst b/Documentation/gpu/rfc/index.rst
> index 91e93a705230..5a3bd3924ba6 100644
> --- a/Documentation/gpu/rfc/index.rst
> +++ b/Documentation/gpu/rfc/index.rst
> @@ -23,3 +23,7 @@ host such documentation:
> .. toctree::
>
> i915_scheduler.rst
> +
> +.. toctree::
> +
> + i915_small_bar.rst
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