OpenVPN using OpenSSL w/Intel's AES-NI Engine-- Performance?

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OpenVPN using OpenSSL w/Intel's AES-NI Engine-- Performance?

Post by Endiel » Tue Aug 31, 2010 5:04 am


As the title implies, I've got two versions of OpenSSL 0.9.8* running on my Intel Westmere system. One has been patched to leverage the AES-NI instructions of the new intel ISA, while the other does not. I've verified that these two work appropriately. Running

"openssl speed --engine aesni -evp aes-128-cbc"

on the optimized executable/library shows significant performance boosts.

So, as a study, I want to see how OpenVPN would benefit from the same thing. I've got two versions-- one that utilizes the AES-NI version of OpenSSL, the other does not. (This is basically the same thing as specifying "--engine aesni" on the command line of OpenVPN as opposed to specifying no engine.) I have created a OpenVPN server/client connection between two computers behind a subnet at a lab here at work, and I've been trying to drive traffic using iperf to show a performance increase with the AES-NI version-- but I simply cannont see any performance boost whatsoever.

I was able to run a simple loopback self-test using the "--test-crypto" command line option built in to OpenVPN along with the "time" command on Linux. Basically, I measured how quickly the two could generate 100000 random packets, starting at 1 byte and going all the way up to 100000 bytes, and loop them back through the encryption and decryption algorithms using aes-128-cbc. Granted, the "--test-crypto" command is doing a number of things besides running aes-128-cbc [such as generating random numbers to fill packets with, etc] but it indicates that we're getting somewhere.

> time openvpn --test-crypto --secret key-regular --verb 0 --tun-mtu 100000 --cipher aes-128-cbc

real 4m58.195s
user 4m57.363s
sys 0m0.000s

> time openvpn --test-crypto --secret key-aesni --verb 0 --tun-mtu 100000 --cipher aes-128-cbc --engine aesni

real 4m14.874s
user 4m14.160s
sys 0m0.000s

You can see that the optimized AES-NI version finishes about 44 seconds faster than the non-optimized version.

Other than that, I have been able to notice no discernible difference using aes-128-cbc, aes-192-cbc, or aes-256-cbc when the engine is engaged as opposed to not engaged while trying to drive traffic over a network between a client and server [both i7 boxes] with iperf. I've even tried running iperf with multiple threads (using the -P option) to no avail.

Does anybody know of a way or perhaps have a clever idea for me to stress test this system to show how AES NI can really juice the performance? I know the RSA key exchange only happens at the beginning, and that everything in between should really be contingent on one of two things:

a) network speed/infastructure
b) how quickly the server can encrypt the data to send it across

What about running multiple copies of the OpenVPN server and having a client/clients attached to each server, all generating iperf traffic at once? I'm just not sure if that would help. I'm at a loss.

It would be really great to realize a situation that allows OpenVPN to significantly benefit from the builtin AES-NI booster instructions on this architecture. However, I'm afraid that the there are other bottlenecks not allowing the AES-NI booster instructions to shine, such as kernel-user level interactions, network link speed, etc. Thus-- your help is greatly appreciated in helping me better understand what might be going on.

I tried muddling with the loopback feature a bit to remove any and all network uncertainty, but that didn't get me anywhere. So far the "--test-crypto" has been the best indication that OpenVPN can indeed benefit from OpenSSL crypto accelerators.

Thank you so much--

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