Matt Turner
66111bc95a
Gen9 and Cherryview have the ability to mark texture instructions with the End-of-thread bit under some conditions, which allows the texture result to be written to the render target directly, rather than returning to the EU. In order to handle overlapping primitives correctly, we have to use the 'sendc' instruction which stalls until other threads potentially writing to the same locations in the render target are retired. Unfortunately, this stall happens before the texture is sampled (rather than in parallel with stall), so for some literal edge cases (like the diagonal edge between two triangles forming a rectangle) there can be a performance penalty. As a result, it's probably not a good idea to use this optimization in general. I had planned to leave it enabled only for BLORP, where we use rectangle primitives and are typically clearing/blitting an entire render target without any overlapping primitives, but I noticed that the optimization wasn't applied in some normal cases anyway. For example, in the piglit test tests/shaders/glsl-fs-texture2d-bias.shader_test it is applied to one BLORP-blit shader but not another due to some kind of mishandling of register types (the destination register type of the texture operation is UD while the color source of the render target write is F). Additionally the instruction scheduler assumed that the combined texture and render target write operation took 0 cycles, leading to cycle estimates that are wildly inaccurate. Since the optimization was not implemented for SIMD32 and our decision whether to use the SIMD32 program is made by comparing the estimated performance with that of the SIMD16 shader, we wrongly threw out a bunch of SIMD32 programs that are likely profitable. total cycles in shared programs: 472807891 -> 473784245 (0.21%) cycles in affected programs: 108277 -> 1084631 (901.72%) helped: 0 HURT: 1290 total sends in shared programs: 998955 -> 1000245 (0.13%) sends in affected programs: 1400 -> 2690 (92.14%) helped: 0 HURT: 1290 LOST: 0 GAINED: 33 This patch shows no performance changes in Intel's Mesa performance CI. Given the problems, the lack of evidence that the pass improves performance, and the fact that the hardware feature was removed from subsequent GPU generations, I think that the pass is not valuable and should be removed. Reviewed-by: Jason Ekstrand <jason@jlekstrand.net> Reviewed-by: Francisco Jerez <currojerez@riseup.net> Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> Signed-off-by: Matt Turner <mattst88@gmail.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5412>
`Mesa <https://mesa3d.org>`_ - The 3D Graphics Library ====================================================== Source ------ This repository lives at https://gitlab.freedesktop.org/mesa/mesa. Other repositories are likely forks, and code found there is not supported. Build & install --------------- You can find more information in our documentation (`docs/install.html <https://mesa3d.org/install.html>`_), but the recommended way is to use Meson (`docs/meson.html <https://mesa3d.org/meson.html>`_): .. code-block:: sh $ mkdir build $ cd build $ meson .. $ sudo ninja install Support ------- Many Mesa devs hang on IRC; if you're not sure which channel is appropriate, you should ask your question on `Freenode's #dri-devel <irc://chat.freenode.net#dri-devel>`_, someone will redirect you if necessary. Remember that not everyone is in the same timezone as you, so it might take a while before someone qualified sees your question. To figure out who you're talking to, or which nick to ping for your question, check out `Who's Who on IRC <https://dri.freedesktop.org/wiki/WhosWho/>`_. The next best option is to ask your question in an email to the mailing lists: `mesa-dev\@lists.freedesktop.org <https://lists.freedesktop.org/mailman/listinfo/mesa-dev>`_ Bug reports ----------- If you think something isn't working properly, please file a bug report (`docs/bugs.html <https://mesa3d.org/bugs.html>`_). Contributing ------------ Contributions are welcome, and step-by-step instructions can be found in our documentation (`docs/submittingpatches.html <https://mesa3d.org/submittingpatches.html>`_). Note that Mesa uses gitlab for patches submission, review and discussions.