Additional paths will be inserted into the search path used for
executables on systems which have a compatible CPU.
Searching $PATH is a slow operation. It is so slow that a shell script
which typically processes many files using utilities from packages
coreutils and/or binutils often factors-out the PATH search by using
shell variables:
CP=$(which cp)
...
$(CP) $file.in $file.out
Do not add directories to $PATH. Any executable which may benefit
significantly from micro-architectural enhancements should use
the IFUNC mechanism explicitly. If the developer of the executable
cannot be bothered to use IFUNC, then the uses of the executable
should not slow down EVERY shell path search in the entire session.
Glibc already uses IFUNC for many mem*() and str*() functions (such as
memcpy, strlen, etc.), which covers the vast majority of "random"
cases which usually benefit from such microarchitecture enhancements.
Fedora binaries for the AMD64 architecture are compiled with
code-generation flags that support almost all CPU variants. But newer
generations of processors gained additional instructions that may be
used to generate faster code. A vendor-independent x86-64 psABI
supplement defines four "microachitecture levels": `x86-64-v1` (the
baseline, our code targets this), `x86-64-v2` (+`SSE3`, CentoOS
targets this), `x86-64-v3` (+`AVX`[edit: and + 'AVX2']), `x86-64-v4`
(+`AVX512`) [1].
Please note the edit: -v3 includes both AVX and AVX2.
There are x86_64 CPUs which have AVX (128-bit xmm registers) but not
AVX2 (256-bit ymm registers): for instance, AMD A10-7890K (cpu family
21, model 56: 4 CPU cores, 8 graphics cores), which was current in 2019.
Why is there no corresponding microarchitecure level? In many cases
AVX2 provides significant benefit over AVX, without the monstrosity
of AVX512 (512-bit zmm registers) which requires vastly more chip area
and power consumption.
--
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