Using
-----
+Environment variables
+~~~~~~~~~~~~~~~~~~~~~
+
+``LP_NATIVE_VECTOR_WIDTH``
+ We can use it to override vector bits. Because sometimes it turns
+ out llvmpipe can be fastest by using 128 bit vectors,
+ yet use AVX instructions.
+``GALLIUM_OVERRIDE_CPU_CAPS``
+ Override cpu capabilities for llvmpipe and softpipe, possible values for x86:
+ `nosse`
+ `sse`
+ `sse2`
+ `sse3`
+ `ssse3`
+ `sse4.1`
+ `avx`
+``GALLIUM_NOSSE``
+ Deprecated in favor of `GALLIUM_OVERRIDE_CPU_CAPS`,
+ use `GALLIUM_OVERRIDE_CPU_CAPS=nosse` instead.
+``LP_FORCE_SSE2``
+ Deprecated in favor of `GALLIUM_OVERRIDE_CPU_CAPS`
+ use `GALLIUM_OVERRIDE_CPU_CAPS=sse2` instead.
+
Linux
~~~~~