[Bug 653611] [NEW] extremely bad dm-crypt latency

[Michael Zugelder]

Public bug reported:

The latency induced by dm-crypt seems to have increased at least five-fold with the Maverick 2.6.35 kernel, compared to the Lucid 2.6.32 kernel.
This makes a very fast SSD system feel like slower than with an HDD.
I did some benchmarks from my current Lucid install with stock kernel and Maverick kernel and was really surprised how slow it really got.

My test system is Ubuntu 10.04 Lucid Lynx x64 on an Intel Core i5 M520 (2.40GHz) Laptop with an Intel X25-V SSD, booting from encrypted root, created with 'cryptsetup luksFormat -c aes-xts-plain -s 256'. The 'aesni_intel' module is loaded and seems to work, since I get well over 250MB/s read/write with an encrypted ramdisk, using various cipher modes (e.g. aes-ecb-plain, aes-cbc-essiv:sha256, aes-xts-plain).
The only difference between the following benchmarks is the booted kernel.

2.6.32:
Linux vpcz1 2.6.32-25-generic #44-Ubuntu SMP Fri Sep 17 20:05:27 UTC 2010 x86_64 GNU/Linux

2.6.35:
Linux vpcz1 2.6.35-22-generic #33-Ubuntu SMP Mon Sep 20 08:11:39 UTC 2010 x86_64

I also just installed the Maverick RC, mounted my encrypted Lucid root
and did some benchmarking, with exactly the same results as using Lucid
with the Maverick 2.6.35 kernel.

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


** Tags: dm-crypt kernel-bug latency regression-release

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extremely bad dm-crypt latency
https://bugs.launchpad.net/bugs/653611
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