AES-NI: Much Faster Encryption & Bitlocker Performance

Westmere (and thus Clarkdale) adds some new instructions to x86, although the big expansion comes with AVX and Sandy Bridge next year. Westmere gets six new encryption/decryption instructions. The group of instructions accelerate AES (Advanced Encryption Standard) and are thus referred to as AES-NI.

Many businesses require that all corporate PCs have the contents of their hard drives encrypted through the use of software like Bitlocker that comes with Microsoft Windows 7. These sorts of applications can be accelerated by AES-NI and to show the potential benefit I dug up a test I did while preparing for one of our SSD articles several months ago.

If you turn on Bitlocker in Windows 7 there's an immediate and measurable impact to performance. Disk performance generally drops by a noticeable amount and actual application usage performance drops by a smaller amount. Every write to the disk has to be encrypted first so there's some obvious CPU overhead. Clarkdale should reduce that overhead significantly as the common encryption operations are now hardware accelerated.

To test this I ran three tests. I first ran PCMark Vantage's HDD suite on my Windows 7 testbed SSD (an OCZ Summit) on a Core i5 661, then encrypted the drive using Bitlocker and ran the same test on the same processor. For the last test I swapped out the i5 661 for a Lynnfield based Core i5 750 (no AES-NI) and re-ran the HDD test. The results below were quite promising:

Processor PCMark Vantage HDD % of Unencrypted Performance
Clarkdale - Unencrypted 16713  
Clarkdale - Bitlocker Encryption 13785 82.5%
Lynnfield - Bitlocker Encryption 11744 70.3%


There's a definite benefit to Clarkdale's AES-NI instructions. There's still a performance hit from enabling Bitlocker, but it's not nearly as great as on Lynnfield and other architectures that don't have AES-NI support. With a smaller decrease in I/O performance from enabling full disk encryption, there's also a smaller hit to application performance as well. This is huge for corporate desktops/notebooks.

Most of those machines aren't quad-core encoding monsters; they use dual-core processors. The upgrade from Core 2 seems like it'd be worth it, or at least AES-NI will probably keep AMD out of the running for consideration.

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  • rainman1986 - Monday, January 4, 2010 - link

    I'm puzzled by the results for this cpu, I'd have thought it would be close to the 920, but it was much slower than the i3 and i5.

    Did I miss something?
  • rainman1986 - Monday, January 4, 2010 - link

    Sorry, not the 860, the 870 was slower (but the 860 would have been just a little slower than that!)

    Still, what gives?
  • deruberhanyok - Monday, January 4, 2010 - link

    Possible responses:

    "I had no idea it had a retro mode!"

    "So these processors can run Ultima IX acceptably then?"

    "My eyes! The goggles, they do nothing!"

    "Intel HD graphics: bringing extreme video quality to 2001's hottest titles!"

    And so on.
  • vol7ron - Monday, January 4, 2010 - link

    The Clarkdale Unencrypted score is shown, could you also display the Lynnfield Unencrypted score.

    To use the unencrypted Clarkdale as the control for Lynnfield doesn't seem right since there are differences between the two procs. It would make more sense to compare
    [Lynnfield Encrypted Score]/[Lynnfield Unencrypted Score] to [Clarkdale Encrypted Score]/[Clarkdale Unencrypted Score]

  • SydneyBlue120d - Monday, January 4, 2010 - link

    Thanks a lot for the great review!

    When You'll be back from CES, I'd like to see a test of:

    - Pentium G9650 (the great absent for the corporate/office world);
    - Flash 10.1 and BR/MKV HTCP with integrated gfx;

    Thanks a lot :-)
  • SydneyBlue120d - Monday, January 4, 2010 - link

    Forgot to ask:

    Is the integrated gfx DX 10 or 10.1? Will it support Direct2D?

  • ruetheday - Friday, January 8, 2010 - link

    yes to DX10 and Direct2D
  • vol7ron - Monday, January 4, 2010 - link


    Good article. I like how you re-addressed topics that you originally discussed on the opening page, with a more concise statement on the pages that followed. For instance, when talking about the memory on/off die. You gave a decent bit of info on page 1 and then a quick rememberance on page 2.

    --- More will come once I finish reading the artice :) ---

  • Rajinder Gill - Monday, January 4, 2010 - link

    Credit goes to Anand for this piece. I only chimed in on the OC side. :)

  • vol7ron - Monday, January 4, 2010 - link

    I noticed something fishy when it said thanks to Raja for the Mobo suggestion. I guess the article's author threw me off :)

    Great collaboration, regardless.

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