Messages in this thread | | | Subject | Re: [PATCH] RFC: dma-buf: Add an API for importing and exporting sync files | From | Christian König <> | Date | Mon, 9 Mar 2020 17:21:19 +0100 |
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Am 05.03.20 um 16:54 schrieb Jason Ekstrand: > On Thu, Mar 5, 2020 at 7:06 AM Christian König <christian.koenig@amd.com> wrote: >> [SNIP] >> Well as far as I can see this won't work because it would break the >> semantics of the timeline sync. > I'm not 100% convinced it has to. We already have support for the > seqno regressing and we ensure that we still wait for all the fences. > I thought maybe we could use that but I haven't spent enough time > looking at the details to be sure. I may be missing something.
That won't work. The seqno regression works by punishing userspace for doing something stupid and undefined.
Be we can't do that under normal circumstances.
>> I can prototype that if you want, shouldn't be more than a few hours of >> hacking anyway. > If you'd like to, go for it. I'd be happy to give it a go as well but > if you already know what you want, it may be easier for you to just > write the patch for the cursor.
Send you two patches for that a few minutes ago. But keep in mind that those are completely untested.
> Two more questions: > > 1. Do you want this collapsing to happen every time we create a > dma_fence_array or should it be a special entrypoint? Collapsing all > the time likely means doing extra array calculations instead of the > dma_fence_array taking ownership of the array that's passed in. My > gut says that cost is ok; but my gut doesn't spend much time in kernel > space.
In my prototype implementation that is a dma_resv function you call and get either a single fence or a dma_fence_array with the collapsed fences in return.
But I wouldn't add that to the general dma_fence_array_init function since this is still a rather special case. Well see the patches, they should be pretty self explaining.
> 2. When we do the collapsing, should we call dma_fence_is_signaled() > to avoid adding signaled fences to the array? It seems like avoiding > adding references to fences that are already signaled would let the > kernel clean them up faster and reduce the likelihood that a fence > will hang around forever because it keeps getting added to arrays with > other unsignaled fences.
I think so. Can't think of a good reason why we would want to add already signaled fences to the array.
Christian.
> > --Jason
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