A bugged TLB on the Opteron / Phenom Posted on 05/12/2007 at 12:53 by Marc
Like all processors, K10s aren’t perfect and there is a certain quantity of defects the majority of which are documented by AMD. However, according to The Tech Report, there is an undocumented defect that is problematic to the extent that AMD has stopped shipping quad core Opterons except in specific OEM contracts.
This erratum causes system hangs when the TLB (Translation Look-aside Buffer, a part of the CPU which accelerates translations between virtual memory addresses and physical memory addresses) is in heavy use, AMD giving the example of virtualization.
The problem can be remedied by an update of the CPU microcode to the motherboard’s bios, but this is to the detriment of performances. In fact, the update deactivates the problematic portion of TLB in L3 cache and consequently reduces its efficiency. The impact on performances in practice should only be a few percentage points in normal applications while in certain specific cases this can attain 10%.
Note that this bug should be definitively resolved via the B3 revision of K10 processors planned for the end of the first quarter of 2008. In the meantime, motherboard manufacturers should quickly offer bios integrating an update of the microcode while AMD will offer to activate or deactivate the erratum’s correction through its AMD Overdrive utility. For the desktop, the risk of system hangs actually seems very low and this is something we didn’t encounter in our tests of the Phenom 9600.
Like all processors, K10s aren’t perfect and there is a certain quantity of defects the majority of which