Re: [Linaro-mm-sig] [PATCH 04/18] dma-fence: prime lockdep annotations

[Jason Gunthorpe]

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