Sorry - I think you may have misread my post? I'm talking about using VBOs for drawing geometry, so there isn't a read command.
Originally Posted by Alfonse Reinheart
That's correct, the GPU should not be modifying the buffer at all in this case, so I would expect the sync to be on the last glBuffer(Sub)Data. But based off the experimentation and performance differences, I think that ATI/AMD on Windows may be syncing with drawing (essentially treating the buffer as having a basic lock, rather than a read-write lock).
Originally Posted by mbentrup