On 17/05/2022 09:29, Tvrtko Ursulin wrote:
On 16/05/2022 19:11, 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.
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: Tvrtko Ursulin tvrtko.ursulin@linux.intel.com Cc: Jon Bloomfield jon.bloomfield@intel.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Jon Bloomfield jon.bloomfield@intel.com 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 | 164 +++++++++++++++++++++++ Documentation/gpu/rfc/i915_small_bar.rst | 47 +++++++ Documentation/gpu/rfc/index.rst | 4 + 3 files changed, 215 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..4079d287750b --- /dev/null +++ b/Documentation/gpu/rfc/i915_small_bar.h @@ -0,0 +1,164 @@ +/**
- 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;
Is -1 possible today or when it will be? For system memory it appears zeroes are returned today so that has to stay I think. Does it effectively mean userspace has to consider both 0 and -1 as unknown is the question.
It looks like it just returns the totalram_pages(). So at the moment nothing ever currently returns -1 or 0. Maybe that was a mistake for I915_MEMORY_SYSTEM.
+ /** + * @unallocated_size: Estimate of memory remaining (-1 = unknown) + * + * Note this is only currently tracked for I915_MEMORY_CLASS_DEVICE + * regions, and also requires CAP_PERFMON or CAP_SYS_ADMIN to get + * reliable accounting. Without this(or if this an older kernel) the
s/if this an/if this is an/
Also same question as above about -1.
This should be the same as above, since this will give the same value as probed_size, or give the real avail value for lmem.
+ * value here will always match 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).
Also question about -1. In this case this could be done since the field is yet to be added but I am curious if it ever can be -1.
I was just going to make this the same as probed_size for system memory. But we could use -1 here instead. What do you think? Same for unallocated below.
+ * + * 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 that if the value returned here is zero, then + * this must be an old kernel which lacks the relevant + * small-bar uAPI support(including
I have noticed you prefer no space before parentheses throughout the text so I guess it's just my preference to have it. Very nitpicky even if I am right so up to you.
Ok, will change :)
+ * 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 currently tracked for + * I915_MEMORY_CLASS_DEVICE regions, and also requires + * CAP_PERFMON or CAP_SYS_ADMIN to get reliable + * accounting. Without this the value here will always + * equal the @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.
Is it defined how rounding up works when a list of regions is given (like smem+lmem) and should that be explicitly mentioned here?
Yes, it uses the largest minimum page-size for the set of regions when doing the round_up. Will tweak.
+ */ + __u64 size;
Blank line here (etc below) maybe to match the previous doc block?
Ok, will tweak. Thanks for the comments and suggestions.
Regards,
Tvrtko
+ /** + * @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 struct + * __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, where usage of this flag results in an error, since + * we lack the relevant small BAR uAPI(see also struct + * __drm_i915_memory_region_info.probed_cpu_visible_size) 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..a322481cea8b --- /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 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