SIMD and compiled code

[ffevotte]

@lungben

Pre-compiled binaries for shipping, however, would either need to be compiled for the lowest common denominator (i.e. not using SIMD capabilities of most modern CPUs to full extend) or require explicit treatment of different SIMD capabilities at runtime, correct?

AFAIU Julia supports an intermediate technique between the two you mention: it can bake into one sysimage several versions of the same code, compiled and optimized for different micro architectures. So that it achieves the best of both worlds: (almost-)fully optimized code and no run-time latency (for what gets baked into the system image).

@lungben

What about the default Julia sysimage? Would it increase runtime speed of (some) base functionality if the sysimage is recompiled on the individual machine, taking its full SIMD capabilities into accout?

As explained in the devdocs, this is what’s used for the default sysimage that is shipped with official pre-built julia releases is compiled.

If you want to use PackageCompiler to produce custom system images for your own packages, you can achieve the same effect (i.e. produce sysimages that are both portable and optimized) using the cpu_target keyword argument to create_sysimage. For example for x86_64 architectures:

create_sysimage(
    packages,
    sysimage_path = "my_sysimage.so",
    # [other kw args]
    cpu_target = "generic;sandybridge,-xsaveopt,clone_all;haswell,-rdrnd,base(1)"
)