On Thu, 9 Jul 2020 at 09:05, Daniel Vetter <daniel@xxxxxxxx> wrote: > On Thu, Jul 09, 2020 at 08:36:43AM +0100, Daniel Stone wrote: > > On Tue, 7 Jul 2020 at 21:13, Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: > > > Comes up every few years, gets somewhat tedious to discuss, let's > > > write this down once and for all. > > > > Thanks for writing this up! I wonder if any of the notes from my reply > > to the previous-version thread would be helpful to more explicitly > > encode the carrot of dma-fence's positive guarantees, rather than just > > the stick of 'don't do this'. ;) Either way, this is: > > I think the carrot should go into the intro section for dma-fence, this > section here is very much just the "don't do this" part. The previous > patches have an attempt at encoding this a bit, maybe see whether there's > a place for your reply (or parts of it) to fit? Sounds good to me. > > Acked-by: Daniel Stone <daniels@xxxxxxxxxxxxx> > > > > > What I'm not sure about is whether the text should be more explicit in > > > flat out mandating the amdkfd eviction fences for long running compute > > > workloads or workloads where userspace fencing is allowed. > > > > ... or whether we just say that you can never use dma-fence in > > conjunction with userptr. > > Uh userptr is entirely different thing. That one is ok. It's userpsace > fences or gpu futexes or future fences or whatever we want to call them. > Or is there some other confusion here?. I mean generating a dma_fence from a batch which will try to page in userptr. Given that userptr could be backed by absolutely anything at all, it doesn't seem smart to allow fences to rely on a pointer to an mmap'ed NFS file. So it seems like batches should be mutually exclusive between arbitrary SVM userptr and generating a dma-fence? Speaking of entirely different things ... the virtio-gpu bit really doesn't belong in this patch. Cheers, Daniel
