[_msw_]

Disclosure: I work at AWS on building cloud infrastructure

C6g instances only launched on June 11. I'm not sure what information can be gleaned from the spot prices regarding Arm demand at this time.

The C5a instances powered by AMD Rome processors have 192 MiB of L3 cache per socket total (16 MiB L3 slice per compute complex, 12 CCX per socket). You can observe this from the cpuid(1) output:

   L3 cache information (0x80000006/edx):
      line size (bytes)     = 0x40 (64)
      lines per tag         = 0x1 (1)
      associativity         = 0x9 (9)
      size (in 512KB units) = 0x180 (384)

384 * 512 KiB = 192 MiB

(you can download cpuid from http://www.etallen.com/cpuid.html)

[lend000]

Thanks for the info -- I must have misinterpreted the spot pricing history chart for c6g. While you're here, does the AWS hypervisor have any means to dedicate a portion of the L3 cache to each virtualized core, or is it a free-for-all for all of the cache space (such that a noisy neighbor could potentially be evicting data held in your L2 cache or even L1 cache by thrashing the L3 cache)?

[_msw_]

For instance families like C, M, and R, processor cores are dedicated to one instance, and the virtual processor is pinned 1:1 to the underlying logical processor. Therefore there is no neighbor that is able to use the L1 and L2 caches.

For L3 cache, we try to optimize for the best overall performance for the majority of the time. Smaller instance sizes share L3 cache with other instances. I wouldn't call it a "free for all" given some changes in how the cache hierarchy has been shifting over time (e.g., Skylake-SP L2 cache per core was increased, and the L3 cache is now 'non-inclusive')