Wednesday, September 13, 2006

AMD to Intel MHz conversions...

While putting together some documentation surrounding physical to virtual migrations, I recalled the following handy formula for approximating Intel MHz from AMD MHz. It's basically a reverse engineered derivation of the formula used by AMD for the Athlon64 'Processor Rating' numbers. Now admittedly, that was part marketing BS, to make them more appealing to Joe User who had been brainwashed by the Intel marketing machine into thinking it was all about the MHz (and boy isn't that coming back to haunt them now!). But the 'Processor Rating' number was close enough to the Intel MHz number that the chips held their own in most benchmarks, so it wasn't complete marketing tripe.

This of course only applies to the older PIII / P4 Xeons - not the latest Woodcrest based chips. But then again, the older PIII / P4 Xeons are the most common targets of P2V migrations, so it works nicely.

The formula is:
(AMD MHz + 500) X 1.5 = Intel MHz

I know you want to confirm it for yourself, so go ahead - here's a list of a few Athlon64 CPU's with their PR & respective MHz numbers.

So, if you had a dual 1.4GHz PIII Xeon box using 20% CPU on average, and you wanted to know what that would equate to on a single 2.2GHz Opteron, you'd do something like:

Dual 1.4GHz PIII Average Workload in MHz:
(1400 X 2) X 20% = 560
Estimated Total Intel Equivalent MHz of Single 2.2GHz Opteron:
(2200 + 500) X 1.5 = 4050
Estimated Percentage CPU Utilisation of Single 2.2GHz Opteron:
560 / 4050 = 13.8%

Of course there is a boatload of confounding variables, such as how optimised the application is for multi procs, is the Opteron dual core, what if that was a Hyperthreaded P4 Xeon instead of a PIII, and all the architectural differences in the chipsets etc etc. While they are all valid questions, I'm just talking about a very basic rule of thumb here. You've gotta draw a line in the sand somewhere, and there's little point in trying to make a guestimate more accurate - in the end, it's still a guestimate.

If anyone else out there knows of a better / more accurate conversion, please post it in the comments!

No comments: