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Implement a simple pre-RA bottom-up list scheduler with the goal of decreasing register pressure. On Xe2, this significantly reduces spilling. SSA form allows us to estimate register demand cheaply and accurately, which theoretically [1] gives this algorithm the two Hippocratic properties: 1. Shaders with low register pressure are unaffected. 2. Register pressure can only be decreased, never increased. In other words: first, do no harm. The heuristic itself is very simple: greedily choose instructions that decrease liveness using a backwards list scheduler. This is far from optimal! But thanks to the above properties, even a heuristic that picked random instructions would be a win overall - by construction, we can only ever win. In other words: this scheduler is your older brother powering off the game console any time he's about to lose a game, maintaining a 100% win rate. [1] In reality, neither property is strictly satisfied due to the messy details of mapping our clean logical model onto Intel's many weird physical register files. Nevertheless, the algorithm is well-motivated and the empirical results on Xe2 are excellent. SIMD16: Totals: Instrs: 2754194 -> 2753957 (-0.01%); split: -0.23%, +0.22% CodeSize: 41094768 -> 41092768 (-0.00%); split: -0.23%, +0.23% Number of spill instructions: 1724 -> 1129 (-34.51%) Number of fill instructions: 1912 -> 1119 (-41.47%) Totals from 168 (6.35% of 2647) affected shaders: Instrs: 850994 -> 850757 (-0.03%); split: -0.75%, +0.73% CodeSize: 12825680 -> 12823680 (-0.02%); split: -0.74%, +0.73% Number of spill instructions: 1724 -> 1129 (-34.51%) Number of fill instructions: 1912 -> 1119 (-41.47%) SIMD32: Totals: Instrs: 4688858 -> 4557800 (-2.80%); split: -3.53%, +0.74% CodeSize: 70177200 -> 68214816 (-2.80%); split: -3.53%, +0.74% Number of spill instructions: 50316 -> 45795 (-8.99%); split: -9.56%, +0.57% Number of fill instructions: 51526 -> 45075 (-12.52%); split: -13.23%, +0.71% Totals from 819 (30.94% of 2647) affected shaders: Instrs: 3810182 -> 3679124 (-3.44%); split: -4.35%, +0.91% CodeSize: 57044000 -> 55081616 (-3.44%); split: -4.35%, +0.91% Number of spill instructions: 49264 -> 44743 (-9.18%); split: -9.76%, +0.58% Number of fill instructions: 50182 -> 43731 (-12.86%); split: -13.58%, +0.73% Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41688> |
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`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.rst <https://docs.mesa3d.org/install.html>`_), but the recommended way is to use Meson (`docs/meson.rst <https://docs.mesa3d.org/meson.html>`_): .. code-block:: sh $ meson setup build $ ninja -C build/ $ sudo ninja -C build/ install Support ------- Many Mesa devs hang on IRC; if you're not sure which channel is appropriate, you should ask your question on `OFTC's #dri-devel <irc://irc.oftc.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.rst <https://docs.mesa3d.org/bugs.html>`_). Contributing ------------ Contributions are welcome, and step-by-step instructions can be found in our documentation (`docs/submittingpatches.rst <https://docs.mesa3d.org/submittingpatches.html>`_). Note that Mesa uses gitlab for patches submission, review and discussions.