-----Original Message----- From: dri-devel dri-devel-bounces@lists.freedesktop.org On Behalf Of Thomas Hellström Sent: Tuesday, February 22, 2022 2:36 AM To: Auld, Matthew matthew.auld@intel.com; intel-gfx@lists.freedesktop.org Cc: Daniel Vetter daniel.vetter@ffwll.ch; dri-devel@lists.freedesktop.org; Kenneth Graunke kenneth@whitecape.org; Bloomfield, Jon jon.bloomfield@intel.com; Justen, Jordan L jordan.l.justen@intel.com; mesa-dev@lists.freedesktop.org Subject: Re: [PATCH 2/2] drm/doc: add rfc section for small BAR uapi
On 2/18/22 12:22, Matthew Auld wrote:
Add an entry for the new uapi needed for small BAR on DG2+.
Signed-off-by: Matthew Auld matthew.auld@intel.com Cc: Thomas Hellström thomas.hellstrom@linux.intel.com Cc: Jon Bloomfield jon.bloomfield@intel.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Jordan Justen jordan.l.justen@intel.com Cc: Kenneth Graunke kenneth@whitecape.org Cc: mesa-dev@lists.freedesktop.org
Documentation/gpu/rfc/i915_small_bar.h | 153
+++++++++++++++++++++++
Documentation/gpu/rfc/i915_small_bar.rst | 40 ++++++ Documentation/gpu/rfc/index.rst | 4 + 3 files changed, 197 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..fa65835fd608 --- /dev/null +++ b/Documentation/gpu/rfc/i915_small_bar.h @@ -0,0 +1,153 @@ +/**
- struct __drm_i915_gem_create_ext - Existing gem_create behaviour,
+with added
- extension support using struct i915_user_extension.
- Note that in the future we want to have our buffer flags here,
Does this sentence need updating, with the flags member?
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 theI915_GEM_CREATE_EXT_MEMORY_REGIONS
* extension to place the object in device local-memory.*/- __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 thekernel 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 platforms where only some of the device* memory is directly visible or mappable through the CPU, like on DG2+.** One of the placements MUST also be I915_MEMORY_CLASS_SYSTEM,to
* ensure we can always spill the allocation to system memory, if we* can't place the object in the mappable part of* I915_MEMORY_CLASS_DEVICE.** Note that buffers that need to be captured withEXEC_OBJECT_CAPTURE,
* will need to enable this hint, if the object can also be placed in* I915_MEMORY_CLASS_DEVICE, starting from DG2+. The execbuf callwill
* throw an error otherwise. This also means that such objects will need* I915_MEMORY_CLASS_SYSTEM set as a possible placement.** Without this hint, the kernel will assume that non-mappable* I915_MEMORY_CLASS_DEVICE is preferred for this object. Note thatthe
* 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.*/+#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 oldgem_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;
+};
+#define DRM_I915_QUERY_VMA_INFO 5
+/**
- struct __drm_i915_query_vma_info
- Given a vm and GTT address, lookup the corresponding vma,
+returning its set
- of attributes.
- .. code-block:: C
- struct drm_i915_query_vma_info info = {};
- struct drm_i915_query_item item = {
.data_ptr = (uintptr_t)&info,
.query_id = DRM_I915_QUERY_VMA_INFO,
- };
- struct drm_i915_query query = {
.num_items = 1,
.items_ptr = (uintptr_t)&item,
- };
- int err;
- // Unlike some other types of queries, there is no need to first query
- // the size of the data_ptr blob here, since we already know ahead of
- // time how big this needs to be.
- item.length = sizeof(info);
- // Next we fill in the vm_id and ppGTT address of the vma we wish
- // to query, before then firing off the query.
- info.vm_id = vm_id;
- info.offset = gtt_address;
- err = ioctl(fd, DRM_IOCTL_I915_QUERY, &query);
- if (err || item.length < 0) ...
- // If all went well we can now inspect the returned attributes.
- if (info.attributes & DRM_I915_QUERY_VMA_INFO_CPU_VISIBLE) ...
- */
+struct __drm_i915_query_vma_info {
- /**
* @vm_id: The given vm id that contains the vma. The id is the value* returned by the DRM_I915_GEM_VM_CREATE. See struct* drm_i915_gem_vm_control.vm_id.*/- __u32 vm_id;
- /** @pad: MBZ. */
- __u32 pad;
- /**
* @offset: The corresponding ppGTT address of the vma which thekernel
* will use to perform the lookup.*/- __u64 offset;
- /**
* @attributes: The returned attributes for the given vma.** Possible values:** DRM_I915_QUERY_VMA_INFO_CPU_VISIBLE - Set if the pagesbacking the
* vma are currently CPU accessible. If this is not set then the vma is* currently backed by I915_MEMORY_CLASS_DEVICE memory, whichthe CPU
* cannot directly access(this is only possible on discrete devices with* a small BAR). Attempting to MMAP and fault such an object will* require the kernel first synchronising any GPU work tied to the* object, before then migrating the pages, either to the CPU accessible* part of I915_MEMORY_CLASS_DEVICE, orI915_MEMORY_CLASS_SYSTEM, if the
* placements permit it. SeeI915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS.
** Note that this is inherently racy.*/+#define DRM_I915_QUERY_VMA_INFO_CPU_VISIBLE (1<<0)
- __u64 attributes;
- /** @rsvd: MBZ */
- __u32 rsvd[4];
+}; diff --git a/Documentation/gpu/rfc/i915_small_bar.rst b/Documentation/gpu/rfc/i915_small_bar.rst new file mode 100644 index 000000000000..fea92d3d69ab --- /dev/null +++ b/Documentation/gpu/rfc/i915_small_bar.rst @@ -0,0 +1,40 @@ +========================== +I915 Small BAR RFC Section +========================== +Starting from DG2 we will have resizable BAR support for device +local-memory, but in some cases the final BAR size might still be +smaller than the total local-memory size. In such cases only part of +local-memory will be CPU accessible, while the remainder is only accessible
via the GPU.
... In such cases only part of local-memory will be CPU accessible/ In such cases, only {small} part of local-memory will be CPU accessible?
+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. +The becomes important when placing an object in LMEM, where
The/This?
+underneath the device has a small BAR, meaning only part 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 LMEM(if
present on the device).
+Related to this, we now also reject any objects marked with +EXEC_OBJECT_CAPTURE, which are also not tagged with
NEEDS_CPU_ACCESS.
+This only impacts DG2+.
+XXX: One open here is whether we should extend the memory region +query to return the CPU visible size of the region. For now the IGTs +just use debugfs to query the size. However, if userspace sees a real +need for this then extending the region query would be a lot nicer.
I guess UMD folks need to comment on this. Although I think since there might be a number of clients utilizing the mappable part, and a number of buffers pinned in there, I figure this might be of limited value outside of tests without some kind of cgroups support.
Otherwise
Acked-by: Thomas Hellström thomas.hellstrom@linux.intel.com
+.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h
- :functions: __drm_i915_gem_create_ext
+DRM_I915_QUERY_VMA_INFO query +----------------------------- +Query the attributes of some vma. Given a vm and GTT offset, find the +respective vma, and return its set of attrubutes. For now we only
Attrubutes/attributes?
You might want to read the document again, and fix punctuations in addition to those typos - at least to make it more legible...
Thanks, ~Akeem
+support DRM_I915_QUERY_VMA_INFO_CPU_VISIBLE, which is set if the +object/vma is currently placed in memory that is accessible by the +CPU. This should always be set on devices where the CPU visible size +of LMEM matches the probed size. If this is not set then CPU faulting +the object will first require migrating the pages.
+.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h
- :functions: __drm_i915_query_vma_info
diff --git a/Documentation/gpu/rfc/index.rst b/Documentation/gpu/rfc/index.rst index 018a8bf317a6..5b8495bdc1fd 100644 --- a/Documentation/gpu/rfc/index.rst +++ b/Documentation/gpu/rfc/index.rst @@ -19,3 +19,7 @@ host such documentation: .. toctree::
i915_scheduler.rst
+.. toctree::
- i915_small_bar.rst