4 ms·

How does that work? The binary format embeds variants of the same program?

• brucethemoose2 3y ago
  On linux distros, the package manager downloads different binaries based on your CPU. Skylake would be x86-64-v3, Zen 4 would be x86-64-v4, for example. And there are different schemes for multiple architectures in the same program, like hwcaps.
  • kergonath 3y ago
    Isn’t this going to get very unmanageable very soon? Intel seems to add extensions every other year or so.
    • jiggawatts 3y ago
      It’s easy to fully automate and storage is relatively cheap these days.
      • xxpor 3y ago
        I'd think the issue would be more build infra, every new variant means you have to build the world again
        • kergonath 3y ago
          Yes. Also, test it.
          • jiggawatts 3y ago
            That can also be largely automated.
            • brucethemoose2 3y ago
              LTO does rarely break things in hard to detect ways, but I have never heard of a -march x86 compilation bug.
        • jiggawatts 3y ago
          Again, compute is surprisingly cheap these days. Work out what it would cost to compile - say - a terabyte of C code at typical cloud spot prices. A large VM with 128 cores can compile the 100 MB Linux kernel source tree in about 30 seconds. So… 200 MB/minute or 12 GB/hour. This would take 80 hours for a terabyte. A 120 core AMD server is about 50c per hour on Azure (Linux spot pricing). So… about $40 to compile an entire distro. Not exactly breaking the bank.
          • xxpor 3y ago
            you'd have to separate out compiling and linking at a bare minimum to get even a semi accurate model. plus a lot of userspace is c++, which is much, much slower.
    • brucethemoose2 3y ago
      The extensions can be kinda broken down into 4 levels. Basically ancient, old (SSE 4.2), reasonably new (AVX2, Haswell/Zen 1 and up), and baseline AVX512. https://developers.redhat.com/blog/2021/01/05/building-red-hat-enterprise-linux-9-for-the-x86-64-v2-microarchitecture-level#background_of_the_x86_64_microarchitecture_levels https://developers.redhat.com/blog/2021/01/05/building-red-h... There is discussion of a fifth level. Someone in the Intel Clear Linux IRC said a fifth level wasn't "worth it" for Sapphire Rapids because most of the new AVX512 extensions were not autovectorized by compilers, but that a new level would be needed in the future. Perhaps they were thinking of APX, but couldn't disclose it.
      • jcranmer 3y ago
        AVX10/APX does sound like a good baseline for v5.
        • Bulat_Ziganshin 3y ago
          except that it doesn't support full AVX-512, making the whole idea of backward compatibility between these levels meaningless. "It's Intel!!!"
          • brucethemoose2 3y ago
            Well that's an even better justification, as a x86-64-v5 level would be needed for the newer CPUs. We can throw away any hope of v4 being a standard baseline.
• slt2021 3y ago
  in the end it will be like any other modern hardware appliance: the hardware is the same design for cost saving purposes, but different features are unlocked for $$$ by a software license key. You want AVX-512? pay up and unlock feature in your CPU and you can now use the feature. This could also enable pay-as-you-go license scheme for CPUs, creating recurring revenue for Intel from the hardware perspective - the same silicon, but different features sold separately
• pjmlp 3y ago
  Yes, here is an example how it works for GCC. https://gcc.gnu.org/onlinedocs/gcc-13.1.0/gcc/Function-Multiversioning.html https://gcc.gnu.org/onlinedocs/gcc-13.1.0/gcc/Function-Multi...