[deathanatos]

> That is a 43% reduction, and it is free: no source change, just a compiler flag.

It's not entirely free; the cost is that the resulting binary will no longer run on processors that lack the instruction. Which, admittedly, is ≈2007 or older. But still! I have a 2012 CPU still in service, and as much as I'd love to obsolete it, gestures at the price tag of RAM these days.

… a 2012 CPU is surprisingly competitive relative to today's tech, too, I'd add. The gap between 2012 and 2026 is nothing compared to the equivalent gap between 1998 and 2012: 1998 is like 500MHz single-core, 32-bit. 2012 is 4 core, 8 hyper threads, 64-bit, 3.5 GHz. (… perhaps more remarkably, my next-oldest machine, a 2017 laptop, is only 2.8 GHz, with the same 4(/8) cores. It also uses like half the power, too. That's mostly the "laptop" bit, though.)

(That same CPU is also incapable of "v3".)

[tgv]

My main problem was that our hosting company offers cheap Linux servers, but with a shared CPU that even doesn't support v2. We pay more now, but you could still run into that problem.

[fweimer]

It's likely this is a hypervisor misconfiguration. Either way, one has to wonder what kind of mitigations for cross-tenant leakage they are missing.

[tgv]

Or on purpose, because the CPUs with AVX are more expensive. Or historical: the hardware for this kind of service may have been old, and you can't tell people that if you buy today you get a processor with AVX, but tomorrow you may get one without. I haven't checked if they upgraded their low-cost options in a while.

[fweimer]

You can try to execute POPCNT. If it does not fault, its presence is only hidden via CPUID.

Live migration support may be the reason why they stick to the baseline. That's most likely to be migratable across different CPU types. Although with a bit of effort, you can figure out what is support by your fleet and configure that into the hypervisors.

I'm skeptical that pre-SSE-4.2 etc. CPUs are economically viable for running customer workloads due to electricity costs.

[rob74]

Either it's a misconfiguration, or it's intentional (only providing a "bare-bones" machine for the lowest price level, even if the underlying hardware would support more)?

[coredog64]

Isn't there a thermal cost to AVX instructions? Or, thinking of other reasons, if you're splitting up physical hardware into a "vCPU", it it possible that AVX doesn't map cleanly?