On 02/05/2022 19:03, Lionel Landwerlin wrote:
On 02/05/2022 20:58, Abodunrin, Akeem G wrote:
-----Original Message----- From: Landwerlin, Lionel G lionel.g.landwerlin@intel.com Sent: Monday, May 2, 2022 12:55 AM To: Auld, Matthew matthew.auld@intel.com; intel-gfx@lists.freedesktop.org Cc: dri-devel@lists.freedesktop.org; Thomas Hellström thomas.hellstrom@linux.intel.com; Bloomfield, Jon jon.bloomfield@intel.com; Daniel Vetter daniel.vetter@ffwll.ch; Justen, Jordan L jordan.l.justen@intel.com; Kenneth Graunke kenneth@whitecape.org; Abodunrin, Akeem G akeem.g.abodunrin@intel.com; mesa-dev@lists.freedesktop.org Subject: Re: [PATCH v2] drm/doc: add rfc section for small BAR uapi
On 20/04/2022 20:13, 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)
Signed-off-by: Matthew Auld matthew.auld@intel.com Cc: Thomas Hellström thomas.hellstrom@linux.intel.com Cc: Lionel Landwerlin lionel.g.landwerlin@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: Akeem G Abodunrin akeem.g.abodunrin@intel.com Cc: mesa-dev@lists.freedesktop.org
Documentation/gpu/rfc/i915_small_bar.h | 190
+++++++++++++++++++++++
Documentation/gpu/rfc/i915_small_bar.rst | 58 +++++++ Documentation/gpu/rfc/index.rst | 4 + 3 files changed, 252 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..7bfd0cf44d35 --- /dev/null +++ b/Documentation/gpu/rfc/i915_small_bar.h @@ -0,0 +1,190 @@ +/**
- 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) */ + __u64 probed_size;
+ /** @unallocated_size: Estimate of memory remaining (-1 = unknown)
*/
+ __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. + */ + __u64 probed_cpu_visible_size; + };
Trying to implement userspace support in Vulkan for this, I have an additional question about the value of probed_cpu_visible_size.
When is it set to -1?
I believe it is set to -1 if it is unknown, and/or not cpu accessible...
Cheers! ~Akeem
So what should I expect on system memory?
I guess just probed_cpu_visible_size == probed_size. Or maybe we can just use -1 here?
What value is returned when all of probed_size is CPU visible on local memory?
probed_size == probed_cpu_visible_size.
Thanks,
-Lionel
I'm guessing before there is support for this value it'll be 0 (MBZ).
After after it should either be the entire lmem or something smaller.
-Lionel
+ }; +};
+/**
- 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. + */ + __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 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 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. + */ +#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; +};
+#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 the
kernel
+ * 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 pages
backing the
+ * vma are currently CPU accessible. If this is not set then the vma is + * currently backed by I915_MEMORY_CLASS_DEVICE memory, which
the 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, or
I915_MEMORY_CLASS_SYSTEM, if the
+ * placements permit it. See
I915_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..be3d9bcdd86d --- /dev/null +++ b/Documentation/gpu/rfc/i915_small_bar.rst @@ -0,0 +1,58 @@ +========================== +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.
+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.
+.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h + :functions: __drm_i915_memory_region_info
+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 attributes. For now we only +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 +probed_cpu_visible_size of I915_MEMORY_CLASS_DEVICE matches the +probed_size. If this is not set then CPU faulting the object will likely first
require migrating the pages.
+.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h + :functions: __drm_i915_query_vma_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 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