[dm-crypt] AES hardware support in dm-crypt / kernel

Jens jens-dmcrypt at spamfreemail.de
Thu Sep 1 23:22:55 CEST 2011


Hello,

I own an ARM-based NAS which - supposedly - has AES hardware support:
The WD MyBook Live. This is the hardware it runs: 
http://myapm.apm.com/MyAMCC/retrieveDocument/PowerPC/
   APM82181/APM82181_PB4090.pdf
The AES modules are also enabled in the current kernel that it runs
(CONFIG_CRYPTO_HW=y).

Upon booting, I get several devices listed in /proc/crypto, but performance
on a test image (mounted via loop, 1GB) is rather low (7..8 MB/s) and 
CPU peaks at 100%. Without encryption the machine can sustain 40..50 MB/s
over GBit ethernet and 80..100 MB/s locally (from /dev/zero).

Am I right that if the crypto hardware were active, the CPU load
during usage of an encrypted device should not be influenced
by the encryption / decryption process
(because this does not happen on the CPU)?
How can I find out for sure whether dm-crypt uses the
hardware acceeleration features?

Thanks!

Jens



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