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Isn’t this going to get very unmanageable very soon? Intel seems to add extensions every other year or so.
by 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 agoIt’s easy to fully automate and storage is relatively cheap these days.
- xxpor 3y agoI'd think the issue would be more build infra, every new variant means you have to build the world again
- kergonath 3y agoYes. Also, test it.
- jiggawatts 3y agoThat can also be largely automated.
- brucethemoose2 3y agoLTO does rarely break things in hard to detect ways, but I have never heard of a -march x86 compilation bug.
- jiggawatts 3y agoAgain, 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 agoyou'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 agoThe 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 agoAVX10/APX does sound like a good baseline for v5.
- Bulat_Ziganshin 3y agoexcept that it doesn't support full AVX-512, making the whole idea of backward compatibility between these levels meaningless. "It's Intel!!!"
- brucethemoose2 3y agoWell 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.