Re: newbie: Speed of loop-aes

Markus Huehnerbein wrote:
> Hi List,
>
> I did some performance tests using the benchmark bonnie++ to evaluate
> different disk encryption possibilities. The results regarding loop-aes
> are a bit strange for my understanding. I ran the tests on a notebook
> with Debian Etch, 1GB RAM and a Linux 2.6.22.2 Kernel.
>
> Bonnie was startet with the following parameters:
> bonnie++ -b -u root -s 4000
>
> As a result loop-aes has a sequential input (block) of 29127 K/sec where
> the sequential input with no encryption is 25123 K/sec. The same with
> sequential output (block) (loop-aes: 27633 K/sec and no encryption:
> 24267 K/sec).
>
> What I don't understand is how encrypted reads and writes per block
> could be faster as plaintext reads / writes? Any comments are welcome!
>
>   
Now I know very little about the bonnie++ benchmark, but it says that

4MB is way to little to show anything. Factors like caching and process 
overhead (which benchmark did you run first?) and other similar factors 
will dominate. Try with at least 4GB. Since the bonnie program test for 
database-like access according to it's website, it will probably not 
make much sense before you test it with file sizes significantly larger 
than the main memory.

If you have not set hdparm, sometimes DMA is not used by the kernel. 
This is the safest on some buggy (but common) mainboards, and may be the 
default on your system. If this is set, non-encrypted writing will be 
much slower than it need to be. Read the manual page for hdparm.

With DMA enabled, the null cipher (that is no encryption) can be as slow 
as an encrypted filesystem, because what slows things down is that the 
block has to be copied into RAM.

> Kind regards,
> Markus
>
> P.S.: The bonnie++ output:
> LOOP-AES:
>  ------Sequential Output------ --Sequential Input- --Random-
>  -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
> Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
> 4000M 18554  59 27633   7 13696   3 18922  77 29127   4 102.3   0
>
> NO ENCRYPTION:
>  ------Sequential Output------ --Sequential Input- --Random-
>  -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
> Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
> 4000M 24085  77 24267   6 11978   3 24825  75 25123   3 103.9   0
>
>
> -
> Linux-crypto:  cryptography in and on the Linux system
> Archive:       http://mail.nl.linux.org/linux-crypto/
>
>   


-
Linux-crypto:  cryptography in and on the Linux system
Archive:       http://mail.nl.linux.org/linux-crypto/