On 2018-02-14 01:15 PM, Christian König wrote: > Am 14.02.2018 um 17:35 schrieb Felix Kuehling: >> [SNIP] >>>>>>> I don't see how you can have separate TTM objects referring to the >>>>>>> same memory. >>>>>> Well that is trivial, we do this all the time with prime and I+A >>>>>> laptops. >>>>> As I understand it, you use DMABuf to export/import buffers on >>>>> multiple >>>>> devices. I believe all devices share a single amdgpu_bo, which >>>>> contains >>>>> the ttm_buffer_object. >>> That's incorrect as well. Normally multiple devices have multiple >>> ttm_buffer_object, one for each device. >>> Going a bit higher that actually makes sense because the status of >>> each BO is deferent for each device. E.g. one device could have the BO >>> in access while it could be idle on another device. >> Can you point me where this is done? I'm looking at >> amdgpu_gem_prime_foreign_bo. It is used if an AMDGPU BO is imported into >> a different AMDGPU device. It creates a new GEM object, with a reference >> to the same amdgpu BO (gobj->bo = amdgpu_bo_ref(bo)). To me this looks >> very much like the same amdgpu_bo, and cosequently the same TTM BO being >> shared by two GEM objects and two devices. > > As Michel pointed out as well that stuff isn't upstream and judging > from the recent requirements it will never go upstream. > >>> If this is enabled by any changes that break existing buffer sharing >>> for >>> A+A or A+I systems, please point it out to me. I'm not aware that this >>> patch series does anything to that effect. >>> As I said it completely breaks scanout with A+I systems. >> Please tell me what "it" is. What in the changes I have posted is >> breaking A+I systems. I don't see it. > > Using the same amdgpu_bo structure with multiple devices is what "it" > means here. That statement seems to contradict this previous statement by you: >>>  What we do is map the same >>> BO in VMs on other devices. It has no effect on GART mappings. > > Correct VM mapping is unaffected here. Can you clarify that contradiction? Is it OK for us to map the same BO in multiple VMs or not? > As I said that concept is incompatible with the requirements on A+A > systems, so we need to find another solution to provide the > functionality. Do you mean you need to find another solution for A+A buffer sharing specifically? Or is this a more general statement that includes the mapping of BOs to multiple VMs on different devices? > What's on my TODO list anyway is to extend DMA-buf to not require > pinning and to be able to deal with P2P. Sounds good. That said, KFD is not using DMABufs here. > > The former is actually rather easy and already mostly done by sharing > the reservation object between exporter and importer. > > The later is a bit more tricky because I need to create the necessary > P2P infrastructure, but even that is doable in the mid term. The sooner you can share your plans, the better. Right now I'm in a bit of limbo. I feel you're blocking KFD upstreaming based on AMDGPU plans and changes that no one has seen yet. Thanks,  Felix > > Regards, > Christian.
