4 ms·

How do cloud vendors handle this on shared machines? Disable AVX?

• w0utert 6y ago
  Not sure how many cloud vendors are running CPU's with AVX-512 support, but I imagine that if they do you either have to pay for exclusive use of a single CPU (all cores), or thath they indeed disable AVX-512 instructions by patching the cpuid flags? Note that the downclocking is only really a problem with AVX-512 and much less so with AVX2 and (AFAIK) not at all with AVX.
• wtallis 6y ago
  The big cloud guys get custom parts with non-standard clock speeds, which may include changes to how AVX512 clocking is handled.
• BeeOnRope 6y ago
  The cloud vendors (at least the ones I checked) have SKUs with fairly limited downclocking, but more importantly the license based downclocking is per-core. So as long as you get at least a core to yourself, the noisy neighbor problem is reduced in that you affect your own CPU speed only. For more fine-grained sharing, sure, if the key before you was running AVX-512 you'll get a lower frequency for the initial part of your timeslice, but it should pop back to full speed in under 1 ms.
  • kristianp 6y ago
    Do the cloud vendors pin their VMs to a core to achieve this?
    • BeeOnRope 6y ago
      Something like that, for the ones that dedicate at least a core per tenant. This also reduces the chance of cross-tenant information leakage. Of course there are lots of scenarios where this isn't the case.