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Consider a simple loop that does a series of texture instructions and
then reduces the results:
vec4 sum = vec4(0);
for (int i = 0; i < N; i++) {
sum += texture(...);
}
Assume that the loop is unrolled and we schedule the resulting basic
block. Right now, after we schedule the first texture instruction, the
only instructions available to schedule that don't incur a sync are the
instructions to setup the second texture instruction. So we keep picking
the texture instructions, no matter how large N is, resulting in a
pathological schedule for register pressure when N is very large:
sum1 = texture(...);
sum2 = texture(...);
sum3 = texture(...);
...
sum = sum1 + sum2 + sum3 + ...;
In particular this happens with some CTS tests for VK_EXT_robustness2,
where a loop like that with many iterations is marked as [[unroll]],
forcing NIR to unroll it.
This solution is a balance between the current approach and always
scheduling for register pressure (and ignoring sync's). We only allow a
certain number of texture fetches to be in flight before considering
textures to "sync", even though they don't really, both because they
likely *will* sync in reality (overflowing the internal queue of waiting
texture instructions) and because at some point we need the normal
algorithm to kick in and start lowering register pressure.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7571>
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| README.rst | ||
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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://mesa3d.org/install.html>`_), but the recommended way is to use Meson (`docs/meson.rst <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.rst <https://mesa3d.org/bugs.html>`_). Contributing ------------ Contributions are welcome, and step-by-step instructions can be found in our documentation (`docs/submittingpatches.rst <https://mesa3d.org/submittingpatches.html>`_). Note that Mesa uses gitlab for patches submission, review and discussions.