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Re: aes-xts-plain with aes_x86_64 makes my SSD 5x slower than my encrypted HD



On Sun, Jul 22, 2012 at 11:28:51PM -0700, Marc MERLIN wrote:
> On Sun, Jul 22, 2012 at 11:47:57PM +0200, Arno Wagner wrote:
> > On Sun, Jul 22, 2012 at 01:39:29PM -0700, Marc MERLIN wrote:
> > > On Sun, Jul 22, 2012 at 09:47:32PM +0200, Yves-Alexis Perez wrote:
> > > > > Any suggestions would be appreciated. 
> > > > 
> > > > I'm using Debian sid (so still at 3.2 kernel), currently using a 256G
> > > > Samsung SSD. What I get is:
> > 
> > SID? That would be "unstable", whit possible assorted problems.


Ok, sorry for my confusion, what kernel/distro are you running?


[...] 
> > Maybe AES-NI needs very long for something it needs to do each 
> > sector. Google("aes-ni slow") found at least some indications that
> > aes-ni may still have problems.
>   
> It was worth a shot, thanks for the suggestion.
> 
> gandalfthegreat:~# lsmod | grep aes
> aes_x86_64             16796  34 
> gandalfthegreat:~# hdparm -t -T /dev/mapper/cryptroot
> 
> /dev/mapper/cryptroot:
>  Timing cached reads:   15802 MB in  2.00 seconds = 7909.98 MB/sec
>  Timing buffered disk reads:  68 MB in  3.04 seconds =  22.39 MB/sec
> gandalfthegreat:~# 
> 
> Unfortunately, speed is exactly the same.
> 
> with aes_x86_64:
> gandalfthegreat:/var/local/VirtualBox VMs/w2k_virtual# dd if=test of=/dev/null
> 4192640+0 records in
> 4192640+0 records out
> 2146631680 bytes (2.1 GB) copied, 12.4848 s, 172 MB/s
> 
> I then rebooted with aesni_intel and got this:
> gandalfthegreat:/var/local/VirtualBox VMs/w2k_virtual# dd if=test of=/dev/null
> 4192640+0 records in
> 4192640+0 records out
> 2146631680 bytes (2.1 GB) copied, 8.42506 s, 255 MB/s

That does not seem to be it. 

> So those speeds are expected/believable, but I still don't know why
> hdparm is so slow on /dev/mapper/cryptroot.
> 
> Mmmh....

Indeed.

Arno
-- 
Arno Wagner,    Dr. sc. techn., Dipl. Inform.,   Email: arno@xxxxxxxxxxx 
GnuPG:  ID: 1E25338F  FP: 0C30 5782 9D93 F785 E79C  0296 797F 6B50 1E25 338F
----
One of the painful things about our time is that those who feel certainty 
are stupid, and those with any imagination and understanding are filled 
with doubt and indecision. -- Bertrand Russell 
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