On Fri, 16 Jul 2021 at 16:23, Jason Ekstrand jason@jlekstrand.net wrote:
On Fri, Jul 16, 2021 at 9:52 AM Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 15/07/2021 11:15, Matthew Auld wrote:
The CPU domain should be static for discrete, and on DG1 we don't need any flushing since everything is already coherent, so really all this does is an object wait, for which we have an ioctl. Longer term the desired caching should be an immutable creation time property for the BO, which can be set with something like gem_create_ext.
One other user is iris + userptr, which uses the set_domain to probe all the pages to check if the GUP succeeds, however we now have a PROBE flag for this purpose.
v2: add some more kernel doc, also add the implicit rules with caching
Suggested-by: Daniel Vetter daniel@ffwll.ch Signed-off-by: Matthew Auld matthew.auld@intel.com Cc: Thomas Hellström thomas.hellstrom@linux.intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Tvrtko Ursulin tvrtko.ursulin@linux.intel.com Cc: Jordan Justen jordan.l.justen@intel.com Cc: Kenneth Graunke kenneth@whitecape.org Cc: Jason Ekstrand jason@jlekstrand.net Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Ramalingam C ramalingam.c@intel.com Reviewed-by: Ramalingam C ramalingam.c@intel.com
drivers/gpu/drm/i915/gem/i915_gem_domain.c | 3 +++ include/uapi/drm/i915_drm.h | 19 +++++++++++++++++++ 2 files changed, 22 insertions(+)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_domain.c b/drivers/gpu/drm/i915/gem/i915_gem_domain.c index 43004bef55cb..b684a62bf3b0 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c @@ -490,6 +490,9 @@ i915_gem_set_domain_ioctl(struct drm_device *dev, void *data, u32 write_domain = args->write_domain; int err;
if (IS_DGFX(to_i915(dev)))return -ENODEV;/* Only handle setting domains to types used by the CPU. */ if ((write_domain | read_domains) & I915_GEM_GPU_DOMAINS) return -EINVAL;diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h index 2e4112bf4d38..04ce310e7ee6 100644 --- a/include/uapi/drm/i915_drm.h +++ b/include/uapi/drm/i915_drm.h @@ -901,6 +901,25 @@ struct drm_i915_gem_mmap_offset {
- I915_GEM_DOMAIN_GTT: Mappable aperture domain
- All other domains are rejected.
- Note that for discrete, starting from DG1, this is no longer supported, and
- is instead rejected. On such platforms the CPU domain is effectively static,
- where we also only support a single &drm_i915_gem_mmap_offset cache mode,
- which can't be set explicitly and instead depends on the object placements,
- as per the below.
- Implicit caching rules, starting from DG1:
- If any of the object placements (see &drm_i915_gem_create_ext_memory_regions)
contain I915_MEMORY_CLASS_DEVICE then the object will be allocated and
mapped as write-combined only.Is this accurate? I thought they got WB when living in SMEM and WC when on the device. But, since both are coherent, it's safe to lie to userspace and say it's all WC. Is that correct or am I missing something?
Yes, it's accurate, it will be allocated and mapped as WC. I think we can just make select_tt_caching always return cached if we want, and it looks like ttm seems to be fine with having different caching values for the tt vs io resource. Daniel, should we adjust this?
A note about write-combine buffer? I guess saying it is userspace responsibility to do it and how.
What exactly are you thinking is userspace's responsibility?
- Everything else is always allocated and mapped as write-back, with the
guarantee that everything is also coherent with the GPU.Haven't been following this so just a question on this one - it is not considered interesting to offer non-coherent modes, or even write combine, with system memory buffers, for a specific reason?
We only care about non-coherent modes on integrated little-core. There, we share memory between CPU and GPU but snooping from the GPU is optional. Depending on access patterns, we might want WB with GPU snooping or we might want WC. I don't think we care about WC for SMEM allocations on discrete. For that matter, I'm not sure you can actually shut snooping off when going across a "real" PCIe bus. At least not with DG1.
--Jason
Regards,
Tvrtko
- Note that this is likely to change in the future again, where we might need
- more flexibility on future devices, so making this all explicit as part of a
*/ struct drm_i915_gem_set_domain { /** @handle: Handle for the object. */
- new &drm_i915_gem_create_ext extension is probable.