Re:Next-Generation IBM POWER10 Processor
by dragontamer on Monday August 17, 2020 @11:21AM
(#24188110)
It should be noted that AES-CBC doesn't have any instruction-level parallelism available.
Both EPYC and Xeons have 2-AES units per core now. But CBC can only effectively use one of them at a time. (Block(n+1) cannot be computed until block(n) is done computing. Because Block(n) is used as input into Block(n+1) in CBC mode).
AES-256-GCM can compute block(n) and block(n+1) simultaneously. So you need to use such a parallel algorithm if you actually want to use the 2x AES pipelines on EPYC or Xeon.
Both EPYC and Xeons have 2-AES units per core now. But CBC can only effectively use one of them at a time. (Block(n+1) cannot be computed until block(n) is done computing. Because Block(n) is used as input into Block(n+1) in CBC mode).
AES-256-GCM can compute block(n) and block(n+1) simultaneously. So you need to use such a parallel algorithm if you actually want to use the 2x AES pipelines on EPYC or Xeon.