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
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