How to fetch the implicit sync fence for a GPU buffer?
Michel Dänzer
michel at daenzer.net
Fri Jun 2 10:29:56 UTC 2023
On 6/1/23 23:15, Hoosier, Matt wrote:
> Hi,
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> In the past there has been writing about Wayland’s model using implicit synchronization of GPU renderbuffers and KMS commits [1] [2].
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> It would sometimes be nice to do that waiting explicitly in a compositor before enqueueing a KMS pageflip that references a buffer who may go on rendering for some time still. This stalls the pipeline.
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> I’m wondering whether there’s an API -- maybe something analogous to drmPrimeHandleToFD() – that allows userspace to fetch a waitable fence fd for a dmabuf?
A dma-buf fd itself can serve this purpose; it polls as readable when the GPU has finished drawing to the buffer.
See https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1880 for how I used this to implement what you describe above in mutter. Note that this involves some Wayland state management challenges for correct operation in all cases though.
--
Earthling Michel Dänzer | https://redhat.com
Libre software enthusiast | Mesa and Xwayland developer
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