[Bug 363763] [NEW] Random access read speed from encrypted filesystem is very slow compared to other linux distributions

[Yakov Hrebtov]

Public bug reported:

Binary package hint: linux-image-server

I have noticed that random-access reads from file located on encrypted filesystem performs very slow -- 2 times slower compared with CentOS 5.3 distribution. There are very high IO wait values during the test.
I have reproduced this issue on different hardware with several ubuntu server kernels: 
 - several 8.04 kernels (last one tested is  2.6.24-23-server)
 - 9.04 RC kernel

I wrote a simple script that creates a 100M file and performs "random-access" reads from it.
The script is attached.

How to reproduce the issue:
1. Create a mapping for encrypted device
   cryptsetup --cipher=aes-cbc-essiv:sha256 --key-size=256 --hash=ripemd160 create cfs1 /dev/sdb
2. Create filesystem
   mkfs.ext3 /dev/mapper/cfs1
3. mkdir /mnt/test; mount /dev/mapper/cfs1 /mnt/test
4. copy attached script to /mnt/test; 
5. Run the script:
   cd /mnt/test; ./random_access.sh
6. compare results with other distributions.

My results are:
1. ubuntu 2.6.24-23-server:
    not encrypted fs: 20 seconds
    encrypted fs: 80 seconds
2. centos 2.6.18-128.el5PAE (similar results on several fedora kernels)
    not encrypted fs: 20 seconds
    encrypted fs: 40 seconds
As you see, ubuntu is two times slower :-(

I'm ready to provide any additional info that can help to solve an
issue.

** Affects: linux-meta (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: dmcrypt iowait kernel

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Random access read speed from encrypted filesystem is very slow compared to other linux distributions
https://bugs.launchpad.net/bugs/363763
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