CPU

Barcelonas and Phenoms, Affected by a More Serious Issue

Rumor has it that the TLB errata might be the least of AMD's problems

By Bogdan Botezatu, Hardware Editor

10th of December 2007, 07:41 GMT

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When things were settling just fine for the two unfortunate chip models from AMD, Phenom and Barcelona, rumors erupt to hit the company yet again. The BIOS patch AMD issued prior to November 19th is alleged to fix the L3 problem at a great performance cost, and there is even an operating system workaround to work at zero performance penalty. Yet, things have started to look even worse for the manufacturers, since word of mouth says there's even a bigger bug with the chips.

On Thursday AMD released a note that said: "There has been some talk about an erratum relative to our TLB cache in Barcelona as well a Phenom processor resulting in delays. AMD notified customers of this erratum and released a BIOS fix prior to the Nov. 19th launch that resolves it." The issue the fix was addressing was number 122, "TLB Flush Filter May Cause Coherency Problem in Multicore Systems."

Things are somewhat different, since a group of persons claim that the 122 issue was not the most critical feature for the chips, and things look even gloomier for Barcelonas and Phenoms. According to them, the real bug is not even publicly documented and is internally referred to as number 298 being alleged to cause random crashes, and not system freeze under heavy workload as the company had stated.

There have been identified two workarounds for the number 298 issue but each has its drawbacks. There is what the sources have suggested:

"1) BIOS-level fix (the 13-20% performance penalty). I've read this errata, it sets two specific hidden registers, surprisingly simple ... which means I'll bet the BIOS-level fix actually disables the L3 cache, the performance penalty is about right.

2) Operating system workaround, word is the performance cost is effectively zero. RedHat has a fix, Microsoft has a fix, VMware (who would take the biggest performance hit) could do one, it's easy to do. Catch is, the OEMs can't guarantee the end customer runs a patched OS, so the OEM would rather wait three months to ship a fixed processor."

So, until the B3 stepping shows off, you may wish to stay away from the K10 architecture. It's still too hot and it is likely that AMD will ultimately issue a recall. We are awaiting for a new year and a fresh start.

TAGS:

AMD | Phenom | Barcelona | Erratum

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