AMD Phenom CPUs are broken

AMD PhenomThe new AMD Phenom and Barcelona Opterons are broken and the only avaliable fix will cost Phenom buyers anywhere between 5% and 50% in performance.

The problem is with the CPU’s translation lookaside buffer (TLB) and L3 cache, and can cause system crashes and even data corruption. AMD have released a patch to fix the problem.

Specifically, Erratum 298 will be described as follows: "The processor operation to change the accessed or dirty bits of a page translation table entry in the L2 from 0b to 1b may not be atomic. A small window of time exists where other cached operations may cause the stale page translation table entry to be installed in the L3 before the modified copy is returned to the L2.

In addition, if a probe for this cache line occurs during this window of time, the processor may not set the accessed or dirty bit and may corrupt data for an unrelated cached operation. The system may experience a machine check event reporting an L3 protocol error has occurred. In this case, the MC4 status register (MSR 0000_0410) will be equal to B2000000_000B0C0F or BA000000_000B0C0F. The MC4 address register (MSR 0000_0412) will be equal to 26h."

The above will probably mean nothing to most people, so Tech Report ran some benchmarks to give a better indication of the real world performance difference between the retail CPUs, before and after the patch to fix the TLB problem. As you can see from the following results, the patch does indeed slow down the new CPUs, sometimes quite considerably:

Bench 1
Bench 2

As you can see the results for Photoshop CS2 are not good at all, and the FireFox results are just shocking. Hopefully AMD can come up with a better fix and not have problems like this pop up in future releases.

[via HardCoreWare]


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Author: GamerNode Staff View all posts by

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