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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - We need fences support in Wayland compositors"
href="https://bugs.freedesktop.org/show_bug.cgi?id=98766#c8">Comment # 8</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - We need fences support in Wayland compositors"
href="https://bugs.freedesktop.org/show_bug.cgi?id=98766">bug 98766</a>
from <span class="vcard"><a class="email" href="mailto:daniel@fooishbar.org" title="Daniel Stone <daniel@fooishbar.org>"> <span class="fn">Daniel Stone</span></a>
</span></b>
<pre>(In reply to James Jones from <a href="show_bug.cgi?id=98766#c7">comment #7</a>)
<span class="quote">> The protocol:
>
> <a href="https://lists.freedesktop.org/archives/wayland-devel/2017-September/035080">https://lists.freedesktop.org/archives/wayland-devel/2017-September/035080</a>.
> html
>
> Doesn't seem to support the persistent object model that would be more
> performant if using something like Vulkan semaphores to perform the
> synchronization, and requires dma-fence. Isn't preferable to write this in
> a way that doesn't require a specific type of primitive and doesn't require
> transmitting/setting up a fence FD on every frame?</span >
We could rewrite it to use a persistent syncobj I suppose, but I don't
understand the performance argument in all honesty. Is it just the overhead of
importing and exporting dma-fences on your driver?
Ultimately we need a dma-fence to work with KMS anyway, so Weston at least
would probably just turn straight around and export the syncobj to a fence if
the client was being displayed in a plane on the display controller. Unless
I've missed something (please point me to it if so?) we also don't have an
extension for EGL to ingest syncobjs, so we'd need export for that anyway.
If the performance argument is just about creating Wayland objects, I'm
intensely relaxed about that. Creating objects does not require a roundtrip,
and we already have a lot of throwaway objects, e.g. in the dmabuf extension
where we create a new object just to take the buffer parameters and discard it
as soon as the buffer is created.</pre>
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