[Ukfreebsd] Disabling hyperthreading on Intel CPUs
jon at axismilton.ltd.uk
Wed Jan 26 12:58:02 GMT 2011
I've done a bit of testing on Intel Hypermarketing I mean Hyperthreading since Apple replaced my Macbook Pro with an i7 one. It has two physical HT cores.
I'm not sure whether it's quite the same as completely disabling the hypercores like you would in the BIOS on a Wintel machine but under OS X there's a tool to control HT and number of cores immediately. The tool clearly controls the OS scheduler.
I've done a few benchmarks flicking switches on the tool, building our code in a VirtualBox, itself configured to have 4 cores also with "make -j <various>".
The build spends most CPU running arm-none-linux-gnueabi-gcc and given the size of the source by the second run it is reasonable that it is cached so we're CPU bound.
For starters I'd say using one or two cores I'd say this machine (2.66GHz i7) is roughly 30% quicker than my E8500 (3GHz Core 2) desktop.
time make -j 2
time make -j 4
time make -j 5
So you might say the virtual cores are worth 20% of a real one.
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