Re: [Intel-gfx] [PATCH 06/10] drm/i915/uapi: add NEEDS_CPU_ACCESS hint

On 5/25/22 20:43, Matthew Auld wrote:

If set, force the allocation to be placed in the mappable portion of I915_MEMORY_CLASS_DEVICE. One big restriction here is that system memory (i.e I915_MEMORY_CLASS_SYSTEM) must be given as a potential placement for the object, that way we can always spill the object into system memory if we can't make space.

Testcase: igt@gem-create@create-ext-cpu-access-sanity-check Testcase: igt@gem-create@create-ext-cpu-access-big 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

---

drivers/gpu/drm/i915/gem/i915_gem_create.c | 26 ++++++--- include/uapi/drm/i915_drm.h | 61 +++++++++++++++++++--- 2 files changed, 71 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_create.c b/drivers/gpu/drm/i915/gem/i915_gem_create.c index d094cae0ddf1..33673fe7ee0a 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_create.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_create.c @@ -241,6 +241,7 @@ struct create_ext { struct drm_i915_private *i915; struct intel_memory_region *placements[INTEL_REGION_UNKNOWN]; unsigned int n_placements;

• unsigned int placement_mask; unsigned long flags; };

@@ -337,6 +338,7 @@ static int set_placements(struct drm_i915_gem_create_ext_memory_regions *args, for (i = 0; i < args->num_regions; i++) ext_data->placements[i] = placements[i];

• ext_data->placement_mask = mask; return 0;

  out_dump:

@@ -411,7 +413,7 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data, struct drm_i915_gem_object *obj; int ret;

• if (args->flags)

• if (args->flags & ~I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS) return -EINVAL;

  ret = i915_user_extensions(u64_to_user_ptr(args->extensions),

@@ -427,13 +429,21 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data, ext_data.n_placements = 1; }

• /*

• * TODO: add a userspace hint to force CPU_ACCESS for the object, which
  

• * can override this.
  

• */
  

• if (ext_data.n_placements > 1 ||

•    ext_data.placements[0]->type != INTEL_MEMORY_SYSTEM)
  

• ext_data.flags |= I915_BO_ALLOC_GPU_ONLY;
  

• if (args->flags & I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS) {

• if (ext_data.n_placements == 1)
  

• 	return -EINVAL;
  

• /*
  

•  * We always need to be able to spill to system memory, if we
  

•  * can't place in the mappable part of LMEM.
  

•  */
  

• if (!(ext_data.placement_mask & BIT(INTEL_REGION_SMEM)))
  

• 	return -EINVAL;
  

• } else {

• if (ext_data.n_placements > 1 ||
  

•     ext_data.placements[0]->type != INTEL_MEMORY_SYSTEM)
  

• 	ext_data.flags |= I915_BO_ALLOC_GPU_ONLY;
  

• }

  obj = __i915_gem_object_create_user_ext(i915, args->size, ext_data.placements,

diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h index e30f31a440b3..5b0a10e6a1b8 100644 --- a/include/uapi/drm/i915_drm.h +++ b/include/uapi/drm/i915_drm.h @@ -3366,11 +3366,11 @@ struct drm_i915_query_memory_regions {

• 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.

• • 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 { /**

@@ -3378,7 +3378,6 @@ struct drm_i915_gem_create_ext { * * The (page-aligned) allocated size for the object will be returned. *

• *
  

  • DG2 64K min page size implications:
  • On discrete platforms, starting from DG2, we have to contend with GTT

@@ -3390,7 +3389,9 @@ struct drm_i915_gem_create_ext { * * Note that the returned size here will always reflect any required * rounding up done by the kernel, i.e 4K will now become 64K on devices

• * such as DG2.
  

• * such as DG2. The kernel will always select the largest minimum
  

• * page-size for the set of possible placements as the value to use when
  

• * rounding up the @size.
  

  • Special DG2 GTT address alignment requirement:

@@ -3414,14 +3415,58 @@ struct drm_i915_gem_create_ext { * is deemed to be a good compromise. */ __u64 size;

• /**
  • @handle: Returned handle for the object.
  • Object handles are nonzero.
  */ __u32 handle;

• /** @flags: MBZ */

• /**

• * @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
  

• * &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 which lack the relevant small-bar uAPI support (see
  

• * also &drm_i915_memory_region_info.probed_cpu_visible_size),
  

• * usage of the flag will result in an error, but 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.

Reviewed-by: Thomas Hellström thomas.hellstrom@linux.intel.com