Re: dm-crypt aes sha512 and I/O performance

["David Brown" <dmlb2000@gmail.com>]

On 7/14/07, David Brown <dmlb2000@gmail.com> wrote:
> I was forced to put full (almost) hard drive encryption on my laptop
> so that all the Open Source Work I get paid to do will be protected in
> case someone tries to steal it and so they won't find any personal
> information about me if they get a hold of my laptop (because every
> idiot keeps their entire life history on their computers).
>
> Besides the futility of the above statement I've been noticing some
> oddities with how linux and dm-crypt handles I/O on the system.
>
> Now normally I get about 30Mb/s write speed I would expect some sort
> of drop in performance due to the encryption but currently I'm getting
> about 9Mb/s write speed and I'm kinda confused as to what the choke
> point is and how to improve the write speed, if it can be.
>
> Currently both my swap and root are encrypted with the default debian
> installer encryption and there's two kcryptd processes running. Now
> from what I've noticed when I'm dumping data to disk they both seem to
> be working, yet I'm not swapping or anything. So am I right to assume
> that the two kcryptd processes are running in parallel encrypting the
> data to the one root device? Also they only seem to be using 20% of
> the processors they are running on, why isn't it 100%? I'm guessing
> that the data isn't being either compressed or blown up when
> encrypting using this encryption style (but I'm not an expert). Would
> making more kcryptd threads increase the I/O speed (more processes
> doing encrypting)? Is there a way to specify more threads of kcryptd?
>
> I'm kinda at a loss, so any help would be appreciated.
> - David Brown

I should remember never to email the LKML during the weekend...

Did anyone see this?

I did some number crunching and with about 15Mb/s read and 9Mb/s write
I end up copying files on the hard drive locally at about 3Mb/s
(rounded). Which is really lame getting twice without encryption was
much better.

I'm using the ata_piix driver in the 2.6.22.1 kernel.

Thanks,
- David Brown
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