Re: [PATCH 5/6] drm/amdgpu: Add flag to disable implicit sync for GEM operations.

["Christian König" <christian.koenig@amd.com>]

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Am 31.10.23 um 15:14 schrieb Michel Dänzer:
> On 10/31/23 14:40, Tatsuyuki Ishi wrote:
>> In Vulkan, it is the application's responsibility to perform adequate
>> synchronization before a sparse unmap, replace or BO destroy operation.
>> Until now, the kernel applied the same rule as implicitly-synchronized
>> APIs like OpenGL, which with per-VM BOs made page table updates stall the
>> queue completely. The newly added AMDGPU_VM_EXPLICIT_SYNC flag allows
>> drivers to opt-out of this behavior, while still ensuring adequate implicit
>> sync happens for kernel-initiated updates (e.g. BO moves).
>>
>> We record whether to use implicit sync or not for each freed mapping. To
>> avoid increasing the mapping struct's size, this is union-ized with the
>> interval tree field which is unused after the unmap.
>>
>> The reason this is done with a GEM ioctl flag, instead of being a VM /
>> context global setting, is that the current libdrm implementation shares
>> the DRM handle even between different kind of drivers (radeonsi vs radv).
> Different drivers always use separate contexts though, even with the same DRM file description, don't they?

Separate contexts don't help here since the VA space is shared between 
the two.

>
> FWIW, RADV will also want explicit sync in the CS ioctl.
You can replace that with the DMA-buf IOCTLs like Faith is planning to 
do for NVK. Regards, Christian.

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