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.a...@intel.com> Cc: Thomas Hellström <thomas.hellst...@linux.intel.com> Cc: Lionel Landwerlin <lionel.g.landwer...@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursu...@linux.intel.com> Cc: Jon Bloomfield <jon.bloomfi...@intel.com> Cc: Daniel Vetter <daniel.vet...@ffwll.ch> Cc: Jon Bloomfield <jon.bloomfi...@intel.com> Cc: Jordan Justen <jordan.l.jus...@intel.com> Cc: Kenneth Graunke <kenn...@whitecape.org> Cc: Akeem G Abodunrin <akeem.g.abodun...@intel.com> Cc: mesa-...@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.rstdiff --git a/Documentation/gpu/rfc/i915_small_bar.h b/Documentation/gpu/rfc/i915_small_bar.hnew 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) thes/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(includingI 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.rstnew 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.rstindex 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
