[Mesa-dev] [PATCH] dri2: Insert a synchronisation point for glXWaitX

[Adam Jackson]

On Wed, 2016-08-17 at 17:50 +0100, Chris Wilson wrote:
> On Wed, Aug 17, 2016 at 12:13:23PM -0400, Adam Jackson wrote:
> > 
> > On Wed, 2016-08-17 at 08:17 -0700, Eric Anholt wrote:
> >  
> > > 
> > > All I'm saying is that it's the thing that was intentionally used for
> > > this purpose in DRI1 and early DRI2, and maybe if it works we shouldn't
> > > just accidentally drop it in a refactor.
> > 
> > I don't see how the patch in this thread does that. I confess I've been
> > looped in on this somewhat late, so if there's another thread I should be
> > looking at for context...
> 
> By calling invalidate on the drawable, before the backend will use the
> surface (either as a texture or as a renderable) it will do a
> DRI2GetBuffers() round trip. (It is also likely that the buffer will
> have been invalidated in the meantime and alreadly pending the round
> trip.) That provides the server with a definite point at which it can
> insert a synchronisation barrier.

I understand that. I don't understand how that counts as "dropping" any
round trips with the server. If anything it's adding one. The patch
does not remove the copy from real to fake front, which request is
already a round trip.

In fact I'd think the ddx ought to treat that copy as a cue to flush X
rendering in any case, since that would also cover the equivalent path
for indirect contexts.

- ajax