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Conclusions
So the BIOS-based workaround for the TLB erratum can have quite an effect on performance. How close were the estimates we've heard of a 10% performance drop? Let's summarize our results and consider the percentage differences.

No TLB patch TLB patch Difference
Sandra cache and memory bandwidth 6527 5932 9.6%
Sandra memory bandwidth - FPU 5403 3650 38.7%
Sandra memory bandwidth - ALU 5401 3648 38.7%
CPU-Z memory access latency 59 99 50.6%
WorldBench - Microsoft Office 2003 SP-1 369 399 7.8%
WorldBench - Adobe Photoshop CS2 521 595 13.3%
WorldBench - Firefox 298 536 57.1%
WorldBench - Microsoft Windows Media Encoder 9.0 248 272 9.2%
WorldBench - WinZip 10 305 321 5.1%
picCOLOR overall score 9.74 7.21 29.9%
Valve Source engine particle simulation benchmark 62 55 12.0%
Valve VRAD map build time 182 191 4.8%
SiSoft Sandra Multimedia Integer x16 130697 130648 0.04%
SiSoft Sandra Multimedia Floating Point x8 169434 169373 0.04%
Total average difference 19.8%
Average difference without memory subsystem tests 13.9%

Across every test we ran, the difference between the Phenom 9600 with and without the TLB patch averages out to 19.8%. However, if we rule out the synthetic memory tests and consider only the application tests, that difference drops to 13.9%.

The most troubling results here are the applications where we see large performance drops with the TLB erratum workaround active, including the Firefox web browser and the picCOLOR image analysis tool. If one happens to spend a lot of time running an application whose memory access patterns don't mix well with the TLB patch, the result could prove frustrating. The BIOS-based workaround for the TLB erratum may achieve its intended result—system stability—but it comes at a pretty steep price in terms of performance.

For the average retail PC consumer, this price might not be unacceptable. After seeing the Firefox test results, I spent some time browsing the web with our Phenom-based test system, and it didn't feel noticeably sluggish to me compared to most modern PCs. Then again, I doubt whether the average sort of consumer is likely to purchase a system with a quad-core processor. One wonders where that leaves AMD and the PC makers currently shipping Phenom-based PCs. I'm not sure a recall is in order, but a discount certainly might be. And folks need to know what they're getting into when purchasing a Phenom 9500 or 9600-based computer this holiday season. Caveat emptor, indeed.

In fact, a credible source indicated to us that at least some of the few high-volume customers who are still accepting Barcelona Opterons with the erratum are receiving "substantial" discounts for taking the chips. One would hope consumers would get the same consideration. The trouble is, I doubt AMD would have shipped Phenom processors in this state were it not feeling intense financial pressure.

AMD's other major concern here should be for its reputation. The company really pulled a no-no by representing Phenom performance to the press (and thus to consumers) without fully explaining the TLB erratum and its performance ramifications at the time of the product's introduction.

As we've reported elsewhere, AMD does plan to fix the TLB erratum with a new revision of its quad-core chip due some time in mid-to-late Q1 of 2008. Once the new revision is available, the Phenom 9500 and 9600 will be replaced by the 9550 and 9650, with the -50 suffix denoting the updated silicon and higher performance. Most users will want to wait until those new Phenom models are available before paying full price for a Phenom processor or a system based on one.TR

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