Mac Pro Westmere Estimating CPU Performance
CPU performance is dependent on many factors:
- The software has a profound influence— software can be single-threaded, or it can use all available CPU cores (rare). See my scorecard.
- Memory speed and amount, caching, etc;
- The technical nature of the computation (eg pure computation, lots of conditional branches, amount of memory access, etc).
- Drive speed — tasks that involve the drive will stall the CPU. A fast SSD is in order for such tasks.
- Configuration — a very few programs are configurable as to how much computing power they use.
My estimations of real-world performance are based on my extensive research over many years with a variety of software and hardware.
The graphs below are illustrative of what can be expected in various real-world scenarios. They are not measurements of specific software or tasks.
Murphy’s Law performance
Murphy’s Law says that the software you use will disappoint: it will be single-threaded, or at best use ~2–3 CPU cores instead of those 4/6/8/12 cores you paid for!
Most software is not written well enough to exploit multiple CPU cores, or uses unfriendly modal processing (eg Photoshop locks you out while it saves or opens, doesn’t let you disable compression, and then insists on using a single CPU core out of the 4/6/8/12 available).
Most software cannot use even 2 cores consistently, let alone 4/6/8/12. Don’t confuse that generality with specific software you might use, or specific tasks within the same application
Note that an iMac 3.6GHz fares rather well in these scenarios: it has a fast clock speed which gives it an advantage for anything that is single-threaded, even over a 8-core or 12-core Mac Pro.
Reasonable expectations for well-written software
This graph is based on running well-written software, meaning that is uses 3-6 CPU cores fairly well. Don’t get your hopes up here, not many programs are well written. Even reasonably well-written software has a hard time using 8 or 12 cores efficiently (utilizing them does not mean utilizing them efficiently in a scalable manner).
What should matter to you is the software you use.
Many photography programs can exploit 3-6 cores for specific operations for short periods of time.This can yield a nice perkiness to certain operations. But don’t expect to see such gains overall.
Best case performance — raw computing potential
You’ll rarely see this in the real world except with special test programs, like MemoryTester.
But a few specialized and very well written programs can come close to these results. If your work involves such program(s), the 12-core machines will have a large positive impact for you.
The reason I call the hexacore 3.33GHz Mac Pro the “sweet spot” should be clear from this graph.