Am 24.08.22 um 18:14 schrieb Jason Ekstrand:
On Mon, Aug 22, 2022 at 8:27 AM Christian König
<christian.koe...@amd.com> wrote:
[SNIP]
>> I suppose it also asks the question around paralleling
>>
>> fd = open()
>> ptr = mmap(fd,)
>> close(fd)
>> the mapping is still valid.
>>
>> I suppose our equiv is
>> handle = bo_alloc()
>> gpu_addr = vm_bind(handle,)
>> gem_close(handle)
>> is the gpu_addr still valid does the VM hold a reference on the
kernel
>> bo internally.
> For Vulkan it looks like this is undefined and the above is not
necessary:
>
> "It is important to note that freeing a VkDeviceMemory object with
> vkFreeMemory will not cause resources (or resource regions) bound to
> the memory object to become unbound. Applications must not access
> resources bound to memory that has been freed."
> (32.7.6)
I'm not sure about this particular question. We need to be sure that
maps get cleaned up eventually. On the one hand, I think it's
probably a valid API implementation to have each mapped page hold a
reference similar to mmap and have vkDestroyImage or vkDestroyBuffer
do an unmap to clean up the range. However, clients may be surprised
when they destroy a large memory object and can't reap the memory
because of extra BO references they don't know about. If BOs unmap
themselves on close or if we had a way to take a VM+BO and say "unmap
this BO from everywhere, please", we can clean up the memory pretty
easily. Without that, it's a giant PITA to do entirely inside the
userspace driver because it requires us to globally track every
mapping and that means data structures and locks. Yes, such an ioctl
would require the kernel to track things but the kernel is already
tracking everything that's bound, so hopefully it doesn't add much.
For both amdgpu as well as the older radeon mapping a BO does *not* grab
a reference to it. Whenever a BO is released all it's mappings just
disappear.
We need to keep track of the mappings anyway to recreate page tables
after (for example) suspend and resume, so that isn't any overhead.
Regards,
Christian.
--Jason
Additional to what was discussed here so far we need an array on
in and
out drm_syncobj for both map as well as unmap.
E.g. when the mapping/unmapping should happen and when it is
completed
etc...
Christian.
>
>
>> Dave.
>>> Dave.
