On Tue, Jun 16, 2020 at 02:07:19PM +0200, Daniel Vetter wrote:
I've pinged a bunch of armsoc gpu driver people and ask them how much this hurts, so that we have a clear answer. On x86 I don't think we have much of a choice on this, with userptr in amd and i915 and hmm work in nouveau (but nouveau I think doesn't use dma_fence in there).
Right, nor will RDMA ODP.
Hm, what's the context here? I thought RDMA side you really don't want dma_fence in mmu_notifiers, so not clear to me what you're agreeing on here.
rdma does not use dma_fence at all, and though it is hard to tell, I didn't notice a dma_fence in the nouveau invalidation call path.
At the very least I think there should be some big warning that dma_fence in notifiers should be avoided.
Ie it is strange that the new totally-not-a-gpu drivers use dma_fence, they surely don't have the same constraints as the existing GPU world, and it would be annoying to see dma_fence notifiers spring up in them
Jason