Re: AMD Phenom: phenomenally slow

by Jeff Hammond-2 :: Rate this Message:

There's quite a bit of discussion online about "erratum" for the
Phenom. The fix is just to disable to TLB
[http://en.wikipedia.org/wiki/Phenom_(processor)] and it causes
significantly a performance hit for some applications
[http://techreport.com/articles.x/13741,http://www.legitreviews.com/article/618/1/].

I'm not an expert, but
http://www.hardcoreware.net/amd-phenom-is-broken-costs-a-14-performance-hit-to-fix/
contains this gem: "The results were even worse than expected. When
looking directly at cache memory performance, bandwidth dropped by as
much as 38.7%, and latency slowed down by over 50%!"

Since BLAS utilizes cache more than the desktop applications I found
results for, it could be that this is sufficient to explain the
problems you see.

Best,

Jeff

On Thu, Jul 3, 2008 at 11:28 AM, M. Edward (Ed) Borasky
<znmeb@...> wrote:

> Clint Whaley wrote:
>> Guys,
>>
>> I just got my hands on a Phenom X4. My understanding was this was the desktop
>> version of the 3rd gen opteron (K10h). I expected it to have the same FPU
>> peak: 4 flops/cycle double SSE, 8 flops/cycle single SSE, 2 flops/cycle x87.
>>
>> However, all my tests indicate it is 2/4/1 (I installed the Goto BLAS as well,
>> and they also run at 1/2 speed compared to opteron). The Athlon-64 was 2/4/2,
>> so it appears to be much crappier than the previous generation hardware.
>> Does anyone have any insight here? The AMD techdocs all lead me to believe
>> 4/8/x (no mention of x87, so crippling that is not as suprising).
>>
>> ?
>> Clint
>>
>> **************************************************************************
>> ** R. Clint Whaley, PhD ** Assist Prof, UTSA ** www.cs.utsa.edu/~whaley **
>> **************************************************************************
>>
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>
> BIOS? Motherboard? RAM? Or do you just need to go ask them for a
> different one?
>
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--
Jeff Hammond
The University of Chicago
http://home.uchicago.edu/~jhammond/

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