Guidance on choosing CPUs

This is a short guide covering some issues concerning modern CPU performance and how to hopefully choose the best CPU for your task.

Clock speed and Single threaded performance

Historically processor performance (at least within the x86 architecture) could be aligned with clockspeed which improved steadily year on year, the '80s and '90s saw CPU performance double every 18-20 months. until the mid 2000s when it seems that chip design hit a number of limits (heat dissipation, die size...) which effectively stalled CPU clock speeds at around 3-4GHz(1). Since then CPU development has largely concentrated on hypertrheading and multicore designs and to a certain extent the server architecture has followed (NUMA). In some cases it appears that single threaded CPU bound apps will actually run slower on newer CPU cores. In a 2011 talk at The Salishan Conference on High Speed Computing Chuck Moore indicated that single threaded performance may actually be decreasing with newer hardware. decpref.png however in the same time multithreaded applications have seen a dramatic increase in system performance with the increases in core density.

We have seen locally similar evidence that

Core density

General Advice

Broadly speaking when purchasing hardware you should consider what kind of applications you are going to run on it. If you are going to be running a small number of single threaded proceses then, particularly if they will be CPU bound, you should consider single processor solutions with the smallest number of cores and the fastest clockspeeds.

Ideally you should test run your application or something similar on existing hardware in the department to see what works best.

It's also worth looking at some performance benchmarking sites as whilst they may not be accurate in terms of absolute perfromance we have found that they are fairly accurate at predicting relative performance between CPUs.


Can I rely on clock speed as an indication of processor speed and thread performance?

Broadly speaking no. All other things being equal a 2.0 GHz core will be faster than a 1.8 GHz core however those other factors include cache size, processor architecture, bus architecture, bus speed, phase of the moon... Other than within a particular processor range it's very dangerous to look at clockspeed and assume that a faster clockspeed with mean better performance. This is especially so with single threaded apps as it appears that recend .


Multi-core and multi-threading performance (the multi-core myth?)

-- IainRae - 03 Aug 2014

  • graphs showing specfloat figures for various CPUs against their release date:


(1) Whist improvements in processor clockspeed have been made through architecture design (bulldozer etc) these architectures also have limits.
Topic attachments
I Attachment Action Size Date Who Comment
pngpng decpref.png manage 87.0 K 25 Aug 2014 - 12:46 IainRae  
pngpng singlethreadedfloat.png manage 80.6 K 04 Aug 2014 - 12:34 IainRae graphs showing specfloat figures for various CPUs against their release date
pngpng singlethreadedint.png manage 74.1 K 04 Aug 2014 - 12:33 IainRae graphs showing specinf figures for various CPUs against their release date
Edit | Attach | Print version | History: r6 < r5 < r4 < r3 < r2 | Backlinks | Raw View | Raw edit | More topic actions...
Topic revision: r5 - 25 Aug 2014 - 12:56:47 - IainRae
This site is powered by the TWiki collaboration platformCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding TWiki? Send feedback
This Wiki uses Cookies