On 23/06/2022 09:57, Lionel Landwerlin wrote:
On 23/06/2022 11:27, Tvrtko Ursulin wrote:
After a vm_unbind, UMD can re-bind to same VA range against an active VM. Though I am not sue with Mesa usecase if that new mapping is required for running GPU job or it will be for the next submission. But ensuring the tlb flush upon unbind, KMD can ensure correctness.
Isn't that their problem? If they re-bind for submitting _new_ work then they get the flush as part of batch buffer pre-amble.
In the non sparse case, if a VA range is unbound, it is invalid to use that range for anything until it has been rebound by something else.
We'll take the fence provided by vm_bind and put it as a wait fence on the next execbuffer.
It might be safer in case of memory over fetching?
TLB flush will have to happen at some point right?
What's the alternative to do it in unbind?
Currently TLB flush happens from the ring before every BB_START and also when i915 returns the backing store pages to the system.
For the former, I haven't seen any mention that for execbuf3 there are plans to stop doing it? Anyway, as long as this is kept and sequence of bind[1..N]+execbuf is safe and correctly sees all the preceding binds. Hence about the alternative to doing it in unbind - first I think lets state the problem that is trying to solve.
For instance is it just for the compute "append work to the running batch" use case? I honestly don't remember how was that supposed to work so maybe the tlb flush on bind was supposed to deal with that scenario?
Or you see a problem even for Mesa with the current model?
Regards,
Tvrtko