Discrepency between AES encryption and performance

poikilos's Avatar


10 Jun, 2018 02:57 AM

I am not sure why there is such a vast difference between Core 2 series Xeon and i7 processors for the AES encryption when their raw processing power is very similar. I have obtained some old servers for free with Xeon processors, and looked up GeekBench results for the maximum speed of processors they each could handle. I was not too suprised that the "high end" (quad-core) processors from several years ago were comparable in performance to my i7 mobile processor (2 cores 4 threads). I was somewhat suprised that the "GeekBench 3 (Single core)" performance on the i7 was about 150% of the speed of the Xeon, but that is understandable considering the "2 threads" per core on my i7. However, I was very surprised and confused at why the "GeekBench 3 (AES single core)" performance differed so much. Here are the examples (I have not purchased the Xeons yet so all of the results are from cpuboss.com which says the data is courtesy of Primate Labs):

The laptop CPU:
"GeekBench 3 (AES single core)": 2,290,000 MB/s

The max speed CPUs avail for (2) old servers:
"GeekBench 3 (AES single core)": 120,650 MB/s
"GeekBench 3 (AES single core)": 136,300 MB/s

I am assuming that AES performance is how fast encryption is done using the CPU. Did cpuboss portray the data from Primate Labs accurately, and if so, is this a glitch or is there some other explanation for why "GeekBench" (and "GeekBench (Multi-Core)") are similar between these 3 processors but "GeekBench 3 (AES single core)" differs by so much for the i7?

  1. 1 Posted by Bert on 29 Dec, 2018 08:18 PM

    Bert's Avatar

    Hi poikilos,
    Your newer i7 supports AES-NI (look it up) a special instruction extension that essentially makes your aes encryption run directly on your hardware. The older CPU you've listed do not support this. As such they need to run it all in software which adds the necessary overhead and runs a lot slower.
    You are only going to need the faster aes if you are running drive encryption or if you have you use a VPN.
    Hope this helps!

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