wl_surface_commit from different thread

Prabhu S prabhusundar at gmail.com
Fri Feb 7 10:57:34 PST 2014

Please find my comments inline.

On Fri, Feb 7, 2014 at 8:18 AM, Jason Ekstrand <jason at jlekstrand.net> wrote:

> Hi Prabhu,
> Could you be a little more specific as to what you are doing.  It sounds
> like you are either writing a client or trying to write the client-side
> wayland bits for a driver stack.  However, it's kind of hard from you
> description to tell exactly what you're working on.  Nevertheless, I will
> try to answer your question as best I can.
=> Adding support to EGL for wayland

> While Weston itself is single-threaded, the libwayland client library can
> handle multiple threads rather well.  Look into wl_event_queue which allows
> you to manage what events get called on what thread.  Also, any request can
> be called from any thread.  The only issue is in the synchronization that
> your app may need to do (know when wl_surface.commit occurs relative to
> wl_shell_surface.set_maximized for instance).  If you want to get a frame
> completion event in another thread, simply call wl_surface.frame,
> wl_surface.commit and then add the callback you got from wl_surface.frame
> to the wl_event_queue for that thread.

> Also, I'm confused by the relationship between your eglSwapBuffers calls
> and your wl_surface.commit calls.  eglSwapBuffers should be calling
> wl_surface.commit before it returns.  Sometimes this means the underlying
> graphics drivers pass sync fences or do other things to keep from doing a
> full glFinish and stalling the GPU. Therefore, in most cases, you shouldn't
> need to be calling wl_surface.commit manually.  Perhaps I'm just
> misunderstanding something?

=> I'm taking reference of dri2_swap_buffers_with_damage from
Assume 3D frame is complex and really takes more time for the 3D GPU to
complete the frame, GPU will be still processing the frame after return
from eglSwapBuffers. I will get notification of the frame completion in
different thread. In my assumption calls following wl_surface.attach,
wl_surface.damage, wl_surface.commit, wl_display.flush need to be called
from in different thread. Can this possible by creating callback and
setevent from different thread(frame completion thread). I assumg
wl_surface.frame is the compositor frame completion event??

> I hope that helps,
> --Jason Ekstrand
> On Fri, Feb 7, 2014 at 8:03 AM, Prabhu S <prabhusundar at gmail.com> wrote:
>> Hello,
>> eglSwapBuffers is a non blocking call. Normally, 3D GPU will be used both
>> for content creation and composition, in that case everything will end up
>> the GPU unit. So the end frame will be will be synchronized. (assuming 1
>> GPU unit).
>> I have a scenario, where 3D GPU being used for creating content and blit
>> engine used for Weston composition. I'm getting frame completion from 3D
>> engine in different thread (not in the same thread eglSwapBuffers calling
>> thread). Currently eglSwapBuffers calling thread need to wait for the frame
>> completion and then call wl_surface_commit to notify Wayland compositor.
>> This takes out most of the performance since GPUs are not active all the
>> time.
>> wl_surface_commit cannot be called from different thread AFAIK. Some
>> advise, suggestions would be appreciated.
>> Thanks
>> Prabhu
>> _______________________________________________
>> wayland-devel mailing list
>> wayland-devel at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/wayland-devel
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