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We don't actually need to extend g0's live range to the EOT message generally - most messages that end a shader are headerless. The main implicit use of g0 is for constructing scratch headers. With the last two patches, we now consider scratch access that may exist in the IR and already extend the liveness appropriately. There is one remaining problem: spilling. The register allocator will create new scratch messages when spilling a register, which need to create scratch headers, which need g0. So, every new spill or fill might extend the live range of g0, which would create new interference, altering the graph. This can be problematic. However, when compiling SIMD16 or SIMD32 fragment shaders, we don't allow spilling anyway. So, why not use allow g0? Also, when trying various scheduling modes, we first try allocation without spilling. If it works, great, if not, we try a (hopefully) less aggressive schedule, and only allow spilling on the lowest-pressure schedule. So, even for regular SIMD8 shaders, we can potentially gain the use of g0 on the first few tries at scheduling+allocation. Once we try to allocate with spilling, we go back to reserving g0 for the entire program, so that we can construct scratch headers at any point. We could possibly do better here, but this is simple and reliable with some benefit. Thanks to Ian Romanick for suggesting I try this approach. fossil-db on Alchemist shows some more spill/fill improvements: Totals: Instrs: 149062395 -> 149053010 (-0.01%); split: -0.01%, +0.00% Cycles: 12609496913 -> 12611652181 (+0.02%); split: -0.45%, +0.47% Spill count: 52891 -> 52471 (-0.79%) Fill count: 101599 -> 100818 (-0.77%) Scratch Memory Size: 3292160 -> 3197952 (-2.86%) Totals from 416541 (66.59% of 625484) affected shaders: Instrs: 124058587 -> 124049202 (-0.01%); split: -0.01%, +0.01% Cycles: 3567164271 -> 3569319539 (+0.06%); split: -1.61%, +1.67% Spill count: 420 -> 0 (-inf%) Fill count: 781 -> 0 (-inf%) Scratch Memory Size: 94208 -> 0 (-inf%) Witcher 3 shows a 33% reduction in scratch memory size, for example. Reviewed-by: Ian Romanick <ian.d.romanick@intel.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30319> |
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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.