Re: [dm-crypt] Poor performane (idle cpu) [SOLVED; problem with "pv"]

[Jakob Sandgren <jakob@southpole.se>]

On Tue, Feb 09, 2010 at 01:28:06AM +0100, Arno Wagner wrote:
> On Tue, Feb 09, 2010 at 12:54:16AM +0100, Jakob Sandgren wrote:
> > Hi,
> > 
> > (please keep me on CC since I'm not subscribed yet)
> > 
> > To me it seems like there is some serious flaw within kcryptd that
> > ends up to wait for "something" instead of sending enough requests to
> > the disks to make sure it has data to decrypt. What do you think?
> 
> The same thing. 
> 
> Here is a reference test (I have notebook disks in this server):
> 
>   Raw read: 54MB/s 14% CPU
>   Read with decrypt: 53MB/s 65% CPU

For reference this is the exact output of my benchmark, maybe there
are some difference in setup or benchmark? 

OOOOOooops! While putting toghether this information I actually found
the cause of the problem, it was my benchark that was wrong!

This was the benchmark I used to get the performance was:
dd if=/dev/mapper/bench1  bs=4M iflag=direct |pv | dd of=/dev/null
and the number reported by "pv" during the run was ~75MB/s and dd
reported the same number when finished.

Changing this to:
dd if=/dev/mapper/bench1  bs=4M iflag=direct of=/dev/null count=1000
gave a more correct number; 125MB/s


I was not aware of that piping the data through pv would cause such a
big degradation in performance.


> That would mean the crypto is pretty slow on your new CPU.
> As a reference, my 53MB/s at 65% CPU is on an 2800MHz Athlon 
> 64 X2 5600+ with aes-cbc-plain. 
> 
> Here is an OpenSSL crypto speed test:
>  openssl speed -evp aes-256-cbc
>  [...]
>  The 'numbers' are in 1000s of bytes per second processed.
>  type           16 bytes     64 bytes    256 bytes   1024 bytes   8192 bytes
>  aes-256-cbc    71848.00k    98649.49k   110187.78k   113646.25k  114666.15k
> 
> You might want to compare this with the numbers on your CPU.

The numbers from my system (Core I7) are below

root@mvh:~#  openssl speed -evp aes-256-cbc
...
The 'numbers' are in 1000s of bytes per second processed.
type             16 bytes     64 bytes    256 bytes   1024 bytes  8192 bytes
aes-256-cbc     110769.28k   118629.67k   120600.15k   121138.86k  121206.10k

I has now been able to get a 175MB/sec from my main raid partition.

Best Regards,
Jakob

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