[Intel-gfx] [PATCH 1/9] drm/doc/rfc: i915 DG1 uAPI
Jason Ekstrand
jason at jlekstrand.net
Mon Apr 26 15:11:18 UTC 2021
On Mon, Apr 26, 2021 at 4:42 AM Matthew Auld <matthew.auld at intel.com> wrote:
>
> Add an entry for the new uAPI needed for DG1. Also add the overall
> upstream plan, including some notes for the TTM conversion.
>
> v2(Daniel):
> - include the overall upstreaming plan
> - add a note for mmap, there are differences here for TTM vs i915
> - bunch of other suggestions from Daniel
> v3:
> (Daniel)
> - add a note for set/get caching stuff
> - add some more docs for existing query and extensions stuff
> - add an actual code example for regions query
> - bunch of other stuff
> (Jason)
> - uAPI change(!):
> - try a simpler design with the placements extension
> - rather than have a generic setparam which can cover multiple
> use cases, have each extension be responsible for one thing
> only
> v4:
> (Daniel)
> - add some more notes for ttm conversion
> - bunch of other stuff
> (Jason)
> - uAPI change(!):
> - drop all the extra rsvd members for the region_query and
> region_info, just keep the bare minimum needed for padding
>
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> Cc: Lionel Landwerlin <lionel.g.landwerlin at linux.intel.com>
> Cc: Jon Bloomfield <jon.bloomfield at intel.com>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Kenneth Graunke <kenneth at whitecape.org>
> Cc: Jason Ekstrand <jason at jlekstrand.net>
> Cc: Dave Airlie <airlied at gmail.com>
> Cc: dri-devel at lists.freedesktop.org
> Cc: mesa-dev at lists.freedesktop.org
> Acked-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> Acked-by: Dave Airlie <airlied at redhat.com>
> ---
> Documentation/gpu/rfc/i915_gem_lmem.h | 212 ++++++++++++++++++++++++
> Documentation/gpu/rfc/i915_gem_lmem.rst | 130 +++++++++++++++
> Documentation/gpu/rfc/index.rst | 4 +
> 3 files changed, 346 insertions(+)
> create mode 100644 Documentation/gpu/rfc/i915_gem_lmem.h
> create mode 100644 Documentation/gpu/rfc/i915_gem_lmem.rst
>
> diff --git a/Documentation/gpu/rfc/i915_gem_lmem.h b/Documentation/gpu/rfc/i915_gem_lmem.h
> new file mode 100644
> index 000000000000..7ed59b6202d5
> --- /dev/null
> +++ b/Documentation/gpu/rfc/i915_gem_lmem.h
> @@ -0,0 +1,212 @@
> +/**
> + * enum drm_i915_gem_memory_class - Supported memory classes
> + */
> +enum drm_i915_gem_memory_class {
> + /** @I915_MEMORY_CLASS_SYSTEM: System memory */
> + I915_MEMORY_CLASS_SYSTEM = 0,
> + /** @I915_MEMORY_CLASS_DEVICE: Device local-memory */
> + I915_MEMORY_CLASS_DEVICE,
> +};
> +
> +/**
> + * struct drm_i915_gem_memory_class_instance - Identify particular memory region
> + */
> +struct drm_i915_gem_memory_class_instance {
> + /** @memory_class: See enum drm_i915_gem_memory_class */
> + __u16 memory_class;
> +
> + /** @memory_instance: Which instance */
> + __u16 memory_instance;
> +};
> +
> +/**
> + * struct drm_i915_memory_region_info - Describes one region as known to the
> + * driver.
> + *
> + * Note that we reserve some stuff here for potential future work. As an example
> + * we might want expose the capabilities(see @caps) for a given region, which
> + * could include things like if the region is CPU mappable/accessible, what are
> + * the supported mapping types etc.
> + *
> + * 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;
> +
> + /** @pad: MBZ */
> + __u32 pad;
> +
> + /** @caps: MBZ */
> + __u64 caps;
> +
> + /** @probed_size: Memory probed by the driver (-1 = unknown) */
> + __u64 probed_size;
> +
> + /** @unallocated_size: Estimate of memory remaining (-1 = unknown) */
> + __u64 unallocated_size;
> +};
> +
> +/**
> + * struct drm_i915_query_memory_regions
> + *
> + * The region info query enumerates all regions known to the driver by filling
> + * in an array of struct drm_i915_memory_region_info structures.
> + *
> + * Example for getting the list of supported regions:
> + *
> + * .. code-block:: C
> + *
> + * struct drm_i915_query_memory_regions *info;
> + * struct drm_i915_query_item item = {
> + * .query_id = DRM_I915_QUERY_MEMORY_REGIONS;
> + * };
> + * struct drm_i915_query query = {
> + * .num_items = 1,
> + * .items_ptr = (uintptr_t)&item,
> + * };
> + * int err, i;
> + *
> + * // First query the size of the blob we need, this needs to be large
> + * // enough to hold our array of regions. The kernel will fill out the
> + * // item.length for us, which is the number of bytes we need.
> + * err = ioctl(fd, DRM_IOCTL_I915_QUERY, &query);
> + * if (err) ...
> + *
> + * info = calloc(1, item.length);
> + * // Now that we allocated the required number of bytes, we call the ioctl
> + * // again, this time with the data_ptr pointing to our newly allocated
> + * // blob, which the kernel can then populate with the all the region info.
> + * item.data_ptr = (uintptr_t)&info,
> + *
> + * err = ioctl(fd, DRM_IOCTL_I915_QUERY, &query);
> + * if (err) ...
> + *
> + * // We can now access each region in the array
> + * for (i = 0; i < info->num_regions; i++) {
> + * struct drm_i915_memory_region_info mr = info->regions[i];
> + * u16 class = mr.region.class;
> + * u16 instance = mr.region.instance;
> + *
> + * ....
> + * }
> + *
> + * free(info);
> + */
> +struct drm_i915_query_memory_regions {
> + /** @num_regions: Number of supported regions */
> + __u32 num_regions;
> +
> + /** @pad: MBZ */
> + __u32 pad;
> +
> + /** @regions: Info about each supported region */
> + struct drm_i915_memory_region_info regions[];
> +};
> +
> +#define DRM_I915_GEM_CREATE_EXT 0xdeadbeaf
> +#define DRM_IOCTL_I915_GEM_CREATE_EXT DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_CREATE_EXT, struct drm_i915_gem_create_ext)
Here's another thought: Instead of burning a new IOCTL number, should
we just re-use DRM_I915_GEM_CREATE? The different structure size
should let us tell the two apart.
--Jason
> +
> +/**
> + * 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, 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: MBZ */
> + __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.
> + */
> +#define I915_GEM_CREATE_EXT_MEMORY_REGIONS 0
> + __u64 extensions;
> +};
> +
> +/**
> + * struct drm_i915_gem_create_ext_memory_regions - The
> + * I915_GEM_CREATE_EXT_MEMORY_REGIONS extension.
> + *
> + * Set the object with the desired set of placements/regions in priority
> + * order. Each entry must be unique and supported by the device.
> + *
> + * This is provided as an array of struct drm_i915_gem_memory_class_instance, or
> + * an equivalent layout of class:instance pair encodings. See struct
> + * drm_i915_query_memory_regions and DRM_I915_QUERY_MEMORY_REGIONS for how to
> + * query the supported regions for a device.
> + *
> + * As an example, on discrete devices, if we wish to set the placement as
> + * device local-memory we can do something like:
> + *
> + * .. code-block:: C
> + *
> + * struct drm_i915_gem_memory_class_instance region_lmem = {
> + * .memory_class = I915_MEMORY_CLASS_DEVICE,
> + * .memory_instance = 0,
> + * };
> + * struct drm_i915_gem_create_ext_memory_regions regions = {
> + * .base = { .name = I915_GEM_CREATE_EXT_MEMORY_REGIONS },
> + * .regions = (uintptr_t)®ion_lmem,
> + * .num_regions = 1,
> + * };
> + * struct drm_i915_gem_create_ext create_ext = {
> + * .size = 16 * PAGE_SIZE,
> + * .extensions = (uintptr_t)®ions,
> + * };
> + *
> + * int err = ioctl(fd, DRM_IOCTL_I915_GEM_CREATE_EXT, &create_ext);
> + * if (err) ...
> + *
> + * At which point we get the object handle in &drm_i915_gem_create_ext.handle,
> + * along with the final object size in &drm_i915_gem_create_ext.size, which
> + * should account for any rounding up, if required.
> + */
> +struct drm_i915_gem_create_ext_memory_regions {
> + /** @base: Extension link. See struct i915_user_extension. */
> + struct i915_user_extension base;
> +
> + /** @pad: MBZ */
> + __u32 pad;
> + /** @num_regions: Number of elements in the @regions array. */
> + __u32 num_regions;
> + /**
> + * @regions: The regions/placements array.
> + *
> + * An array of struct drm_i915_gem_memory_class_instance.
> + */
> + __u64 regions;
> +};
> diff --git a/Documentation/gpu/rfc/i915_gem_lmem.rst b/Documentation/gpu/rfc/i915_gem_lmem.rst
> new file mode 100644
> index 000000000000..462f1efd9003
> --- /dev/null
> +++ b/Documentation/gpu/rfc/i915_gem_lmem.rst
> @@ -0,0 +1,130 @@
> +=========================
> +I915 DG1/LMEM RFC Section
> +=========================
> +
> +Upstream plan
> +=============
> +For upstream the overall plan for landing all the DG1 stuff and turning it for
> +real, with all the uAPI bits is:
> +
> +* Merge basic HW enabling of DG1(still without pciid)
> +* Merge the uAPI bits behind special CONFIG_BROKEN(or so) flag
> + * At this point we can still make changes, but importantly this lets us
> + start running IGTs which can utilize local-memory in CI
> +* Convert over to TTM, make sure it all keeps working. Some of the work items:
> + * TTM shrinker for discrete
> + * dma_resv_lockitem for full dma_resv_lock, i.e not just trylock
> + * Use TTM CPU pagefault handler
> + * Route shmem backend over to TTM SYSTEM for discrete
> + * TTM purgeable object support
> + * Move i915 buddy allocator over to TTM
> + * MMAP ioctl mode(see `I915 MMAP`_)
> + * SET/GET ioctl caching(see `I915 SET/GET CACHING`_)
> +* Add pciid for DG1 and turn on uAPI for real
> +
> +New object placement and region query uAPI
> +==========================================
> +Starting from DG1 we need to give userspace the ability to allocate buffers from
> +device local-memory. Currently the driver supports gem_create, which can place
> +buffers in system memory via shmem, and the usual assortment of other
> +interfaces, like dumb buffers and userptr.
> +
> +To support this new capability, while also providing a uAPI which will work
> +beyond just DG1, we propose to offer three new bits of uAPI:
> +
> +DRM_I915_QUERY_MEMORY_REGIONS
> +-----------------------------
> +New query ID which allows userspace to discover the list of supported memory
> +regions(like system-memory and local-memory) for a given device. We identify
> +each region with a class and instance pair, which should be unique. The class
> +here would be DEVICE or SYSTEM, and the instance would be zero, on platforms
> +like DG1.
> +
> +Side note: The class/instance design is borrowed from our existing engine uAPI,
> +where we describe every physical engine in terms of its class, and the
> +particular instance, since we can have more than one per class.
> +
> +In the future we also want to expose more information which can further
> +describe the capabilities of a region.
> +
> +.. kernel-doc:: Documentation/gpu/rfc/i915_gem_lmem.h
> + :functions: drm_i915_gem_memory_class drm_i915_gem_memory_class_instance drm_i915_memory_region_info drm_i915_query_memory_regions
> +
> +GEM_CREATE_EXT
> +--------------
> +New ioctl which is basically just gem_create but now allows userspace to
> +provide a chain of possible extensions. Note that if we don't provide any
> +extensions then we get the exact same behaviour as gem_create.
> +
> +Side note: We also need to support PXP[1] in the near future, which is also
> +applicable to integrated platforms, and adds its own gem_create_ext extension,
> +which basically lets userspace mark a buffer as "protected".
> +
> +.. kernel-doc:: Documentation/gpu/rfc/i915_gem_lmem.h
> + :functions: drm_i915_gem_create_ext
> +
> +I915_GEM_CREATE_EXT_MEMORY_REGIONS
> +----------------------------------
> +Implemented as an extension for gem_create_ext, we would now allow userspace to
> +optionally provide an immutable list of preferred placements at creation time,
> +in priority order, for a given buffer object. For the placements we expect
> +them each to use the class/instance encoding, as per the output of the regions
> +query. Having the list in priority order will be useful in the future when
> +placing an object, say during eviction.
> +
> +.. kernel-doc:: Documentation/gpu/rfc/i915_gem_lmem.h
> + :functions: drm_i915_gem_create_ext_memory_regions
> +
> +One fair criticism here is that this seems a little over-engineered[2]. If we
> +just consider DG1 then yes, a simple gem_create.flags or something is totally
> +all that's needed to tell the kernel to allocate the buffer in local-memory or
> +whatever. However looking to the future we need uAPI which can also support
> +upcoming Xe HP multi-tile architecture in a sane way, where there can be
> +multiple local-memory instances for a given device, and so using both class and
> +instance in our uAPI to describe regions is desirable, although specifically
> +for DG1 it's uninteresting, since we only have a single local-memory instance.
> +
> +Existing uAPI issues
> +====================
> +Some potential issues we still need to resolve.
> +
> +I915 MMAP
> +---------
> +In i915 there are multiple ways to MMAP GEM object, including mapping the same
> +object using different mapping types(WC vs WB), i.e multiple active mmaps per
> +object. TTM expects one MMAP at most for the lifetime of the object. If it
> +turns out that we have to backpedal here, there might be some potential
> +userspace fallout.
> +
> +I915 SET/GET CACHING
> +--------------------
> +In i915 we have set/get_caching ioctl. TTM doesn't let us to change this, but
> +DG1 doesn't support non-snooped pcie transactions, so we can just always
> +allocate as WB for smem-only buffers. If/when our hw gains support for
> +non-snooped pcie transactions then we must fix this mode at allocation time as
> +a new GEM extension.
> +
> +This is related to the mmap problem, because in general (meaning, when we're
> +not running on intel cpus) the cpu mmap must not, ever, be inconsistent with
> +allocation mode.
> +
> +Possible idea is to let the kernel picks the mmap mode for userspace from the
> +following table:
> +
> +smem-only: WB. Userspace does not need to call clflush.
> +
> +smem+lmem: We allocate uncached memory, and give userspace a WC mapping
> +for when the buffer is in smem, and WC when it's in lmem. GPU does snooped
> +access, which is a bit inefficient.
> +
> +lmem only: always WC
> +
> +This means on discrete you only get a single mmap mode, all others must be
> +rejected. That's probably going to be a new default mode or something like
> +that.
> +
> +Links
> +=====
> +[1] https://patchwork.freedesktop.org/series/86798/
> +
> +[2] https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5599#note_553791
> diff --git a/Documentation/gpu/rfc/index.rst b/Documentation/gpu/rfc/index.rst
> index a8621f7dab8b..05670442ca1b 100644
> --- a/Documentation/gpu/rfc/index.rst
> +++ b/Documentation/gpu/rfc/index.rst
> @@ -15,3 +15,7 @@ host such documentation:
>
> * Once the code has landed move all the documentation to the right places in
> the main core, helper or driver sections.
> +
> +.. toctree::
> +
> + i915_gem_lmem.rst
> --
> 2.26.3
>
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