[Mesa-dev] [EGL android: accquire fence implementation] i965: Queue the buffer with a sync fence for Android OS

[Michel Dänzer]

On 13/07/17 09:28 AM, Wu, Zhongmin wrote:
> Hi Tomasz
> 
> Thanks,  but I am afraid we have to use the last fence from the last buffer flushing , According to my understanding:
> 
> If the glFlush was called before swapbuffer ,    there would be no new fence after that since the batch buffer may be flushed out, no batch flushing, no fence generated.
> 
> ====
> You can check the function "_intel_batchbuffer_flush_fence",  at the very beginning, it will check the content of the buffer, if it is empty, it will return and do nothing.
> =====
> 
> So, as the same reason,  it may not work if we use dri2_dpy->fence->create_fence_fd,   the process is below.
> 
> Swapbuffer (==> flush batch buffer) ==>  create_fence_fd(===> flush batch buffer and get fd)
> 
> You can see, the second buffer flushing may get nothing (not to mention  the first buffer flushing may get nothing either)

Apologies for jumping into this discussion, and possibly missing some
context.

FWIW, it should be possible to re-use the previous fence when there is
no new work to flush. See e.g. commits

f1be3d8cdde1 ("radeonsi: don't flush an empty IB if the only thing we
               need is a fence")
800efb0690e9 ("radeonsi: Flush when we're asked to return a fence but
               don't have one yet")

for how the radeonsi driver handles this.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer