[Mesa-dev] Plumbing explicit synchronization through the Linux ecosystem

Adam Jackson ajax at redhat.com
Thu Mar 19 15:45:00 UTC 2020

On Tue, 2020-03-17 at 10:12 -0700, Jacob Lifshay wrote:
> One related issue with explicit sync using sync_file is that combined
> CPUs/GPUs (the CPU cores *are* the GPU cores) that do all the
> rendering in userspace (like llvmpipe but for Vulkan and with extra
> instructions for GPU tasks) but need to synchronize with other
> drivers/processes is that there should be some way to create an
> explicit fence/semaphore from userspace and later signal it. This
> seems to conflict with the requirement for a sync_file to complete in
> finite time, since the user process could be stopped or killed.

DRI3 (okay, libxshmfence specifically) uses futexes for this. Would
that work for you? IIRC the semantics there are that if the process
dies the futex is treated as triggered, which seems like the only
sensible thing to do.

- ajax

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