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Phenom loses up to 80 percent due to TLB bug

Phenom loses up to 80 percent due to TLB bug

AMD's long-awaited start of its new processor generation based on the “Barcelona” architecture, including its Agena (-FX) offshoot in the form of the Phenom desktop processors, is becoming more and more of the recently known bug in the translation look-aside Buffer for the L3 cache overshadows.

First performance comparisons by our colleagues at TechReport.com have now shown that the workaround published by AMD, which is supposed to circumvent this bug by deactivating critical areas of the TLB, Depending on the application, performance losses of up to 80 percent can be accepted.

Benchmark without patch with patch difference SiSoft Sandra Cache & Memory 6527 MB/s 5932 MB/s 9.1% SiSoft Sandra Memory FPU 5403 MB/s 3650 MB/s 32.4% SiSoft Sandra Memory Int 5401 MB/s 3648 MB/s 32.5% CPU-Z Memory Access Latency 59 ns 99 ns 67.8% WorldBench MS Office 2003 369 s 399 s 8.1% WorldBench Adobe Photoshop CS2 521 s 595 s 14.2% Worldbench Firefox 298 s 536 s 79.9% WorldBench MS Windows Media Encoder 9.0 248 s 272 s 9.7% WorldBench WinZip 10 305 s 321 s 5.3% picCOLOR Score 9.74 s 7.21 s 25.9% Valve Source Engine Particle Simulation 62 fps 55 fps 11.3% Valve VRAD Map Build Time 182 s 191 s 5.0% SiSoft Sandra Multimedia Int x16 130697 it/s 130648 it/s 0.04% SiSoft Sandra Multimedia FP x8 169434 it/s 169373 it/s 0.04%

All results TechReport. com

At first glance, the drastically reduced memory throughputs appear particularly bitter, which, thanks to the integrated memory controller, have undoubtedly been one of the absolute strengths of AMD in recent years. The result in the Firefox benchmark is just as tragicfrom WorldBench, where the Phenom has lost more than 50 percent of its performance due to the patch. Photoshop and picCOLOR also fare above average here. In purely theoretical applications, the bug has so far had practically no effect. Averaged over the range of applications, the loss is almost 20 percent. If you take the theoretical memory tests out of the calculation, it is still a good 10 percent that the Phenom loses after the patch has been applied.

Owners of a Phenom or Opteron based on the affected B2 stepping are spoiled for choice in view of these sometimes quite clear cuts: Either you risk a system crash as a result of the TLB bug or sometimes you do without more in some applications than half the performance. The bug in the translation lookaside buffer, which apparently occurs with the use of the new feature “nested page tables” in virtual machines, caused AMD to stop delivering the Barcelona-based Opterons in B2 stepping for the time being. Phenom, AMD's desktop quad-core processor is not affected by this delivery stop. Probably because the 'nested page tables' are almost not used there.

Update

Because there are differences between the measurement results with and without TLB -Patch came to numerous inconsistencies, we recalculated the difference values ​​accordingly and updated them in the news. The values ​​are now determined according to the formula (Without Patch/With Patch - 1) * 100. According to this, the losses instead of 50% even in the case of Mozilla Firefox are up to 80% and thus worsen the picture even more.

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