This implements most of the remaining u_threaded_context support. Most
of the heavy lifting was done in the previous patches which fixed things
up for the new thread safety requirements. Only a few things remain.
u_threaded_context support can be disabled via an environment variable:
GALLIUM_THREAD=0
On Felix's Tigerlake with the GPU at fixed frequency, enabling
u_threaded_context improves performance of several games:
- Civilization VI: +17%
- Shadow of Mordor: +6%
- Bioshock Infinite +6%
- Xonotic: +6%
Various microbenchmarks improve substantially as well:
- GfxBench5 gl_driver2: +58%
- SynMark2 OglBatch6: +54%
- Piglit drawoverhead: +25%
Reviewed-by: Zoltán Böszörményi <zboszor@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8964>
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