On Tuesday, October 14, 2014 04:42:39 PM Kenneth Graunke wrote: > According to INTEL_DEBUG=perf, "Borderlands: The Pre-Sequel" was > stalling on nearly every glBufferSubData call, with very slightly > overlapping busy ranges. > > It turns out the draw upload code was accidentally including an extra > stride's worth of data in the vertex buffer size due to a simple > off-by-one error. We considered this extra bit of buffer space to be > busy (in use by the GPU), when it was actually idle. > > The new diagram should make it easier to understand the formula. It's > basically what I drew on paper when working through an actual > glDrawRangeElements call. > > Eliminates all glBufferSubData stalls in "Borderlands: The Pre-Sequel." > > Signed-off-by: Kenneth Graunke <kenn...@whitecape.org> > Cc: mesa-sta...@lists.freedesktop.org > --- > src/mesa/drivers/dri/i965/brw_draw_upload.c | 22 +++++++++++++++++++++- > 1 file changed, 21 insertions(+), 1 deletion(-) > > No Piglit regressions on Haswell. This might help Dota 2 and Serious Sam 3 > as well, but I haven't checked.
Chris Forbes asked me for actual performance numbers, so here they are: the initial sequence is roughly 1.6x to 1.8x faster. (I measured FPS by typing `stat fps` in the developer console and eyeballing the FPS counter it displayed in the corner. Not the most scientific, but when the change is large enough...it works.)
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