[RFC PATCH 3/5] drm/amdgpu: Allow explicit sync for VM ops.

[Christian König]

Am 24.06.22 um 22:34 schrieb Daniel Vetter:
> Digging out of a hole, apologies to everyone.

No problem, I'm totally overworked as well.

> On Fri, Jun 17, 2022 at 03:08:00PM +0200, Christian König wrote:
>> Am 17.06.22 um 15:03 schrieb Bas Nieuwenhuizen:
>>> [SNIP]
>> BOOKKEEP is exactly for that, but as discussed with Daniel that's not what
>> we want in the kernel.
> Not sure which Daniel you talked to, but this wasn't me.

Hui what? Of course I'm talking about you.

>> When you mix implicit with explicit synchronization (OpenGL with RADV for
>> example) it should be mandatory for the OpenGL to wait for any RADV
>> submission before issuing an operation.
>>
>> What you want to do is intentionally not supported.
> vk is very intentional in it's rejecting of any implicit sync.

[SNIP]

> We should probably also document this in the kerneldoc for the BOOKKEEPING
> usage that this is the fence type that vulkan cs should use in all
> drivers, otherwise this will become an endless mess of driver specific
> hacks (i.e. the world we currently live in).

Well, Daniel somehow we are somehow not talking about the same thing here :)

I've documented exactly what you describe above in the initial patch 
which added BOOKKEEPING (I've still called it OTHER in that iteration):

> >/+ /**/
> >/+ * @DMA_RESV_USAGE_OTHER: No implicit sync./
> >/+ */
> >/+ * This should be used for operations which don't want to add an/
> >/+ * implicit dependency at all, but still have a dependency on memory/
> >/+ * management./
> >/+ */
> >/+ * This might include things like preemption fences as well as device/
> >/+ * page table updates or even userspace command submissions./
> >/+ */
> >/+ * The kernel memory management *always* need to wait for those fences/
> >/+ * before moving or freeing the resource protected by the dma_resv/
> >/+ * object./
> >/+ *//
> >/+ DMA_RESV_USAGE_OTHER/

Later on I've even explicitly mentioned that this is for Vulkan submissions.

But it was *you* who made me remove that with the explanation that we 
have to use READ for that or we break existing userspace.

I mean that still makes a lot of sense to me because if I'm not 
completely mistaken we do have use cases which break, especially 
Vulkan+encoding.

Regards,
Christian.

> -Daniel
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