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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  • Marcin - Monday, January 4, 2010 - link

    2D load
  • Anand Lal Shimpi - Monday, January 4, 2010 - link

    The Radeon HD 5870 is quite power efficient if it's not running a 3D app. Our load tests were done using our x264 encoding benchmark to stress the CPU. That's why I used the 5870 as a companion in those benchmarks - makes overall system power consumption lower so we can better see differences between CPUs. Good job AMD :)

    Take care,
  • yacoub - Monday, January 4, 2010 - link

    Intel gives us this crap instead of 32nm P55.
  • DrMrLordX - Monday, January 4, 2010 - link

    Can we see results on an i3 530 instead? Some people with ES chips are reporting that i3s are not good for much of anything over 4 ghz. Also, the vcore on your 4.8 ghz is pretty high, even with water cooling. I would not want to run an i3 at that vcore on a daily basis.

    The phase results are really interesting, but I have to wonder how well this chip scales given the memory speed limitations you run into at higher BCLK.
  • Spoelie - Monday, January 4, 2010 - link

    First CPU-Z screenshot on the overclocking page shows CPU @ 1.3GHz, I don't think this is the correct shot?
  • Rajinder Gill - Monday, January 4, 2010 - link

    Speedstep and Turbo enbaled. The full load speed is 26X149 BCLK, so around 3874MHz..
  • Spoelie - Monday, January 4, 2010 - link

    True, comment on gaming benchmarks:
    " the Core i3s are good gaming chips - especially when you consider how far you can overclock them. "

    But how would you know, not having any in-house?
  • Anand Lal Shimpi - Monday, January 4, 2010 - link

    I've heard some very good initial results but I will be able to confirm when I get back from CES :)

    Take care,
  • marc1000 - Monday, January 4, 2010 - link

    Suddenly it all makes sense. Intel would never enable 1080p decoding on Atom D510 not because of technical issues, but simply because it would kill the market for i3 even before it was released. The HTPC market does not need the i3 brute-power, but this is the only platform that will have HDMI and 1080p. If Atom D510 could do 1080p and had HDMI output then the choice for a HTPC would be a no-brainer. And excuse me, but I already have a gaming rig, so all I want right now is a HTPC to play PC content on my TV. And I won't buy a core i3 to do that, but I would buy a decent Atom board if it had the required HDMI and 1080p... so, for me, no HTPC for now...
  • Kjella - Monday, January 4, 2010 - link

    That is why the old Atom + ION exists, excellent setup with 1080p acceleration and HDMI out. If you don't want it, wait until AMD or VIA/nVidia manages to work something out.

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