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connclark November 6, 2007 13:57

I thought I might mention this
I thought I might mention this here. The Linux kernel since 2.6.12 has implemented as security enhancement called Address Space Layout Randomization (see for a description). This basically randomizes the address locations that it loads code, data, and stack memory. This has the unwanted side effect of increasing the number of page directories for memory management and thus reducing processor TLB hits (Refer to the second half of section 6.2.4 here ).

Now for the performance tweak. You can disable ASLR by adding the kernel boot parameter norandmaps . This does make your system theoretically less secure however if you have your system on a relatively safe network you may judge it to be worth doing. I haven't benchmarked any OpenFOAM runs with this yet. I did benchmark 5 kernel compiles with and with out it and had a consistent 0.25% speed increase. Considering the amount of memory that OpenFOAM uses with large cases I would expect that this speed increase would be higher.

Try it and see

connclark November 6, 2007 19:54

Update: I did a benchmark done
Update: I did a benchmark done with the tutorial channelOodles case.

with ASLR it took 110 minutes and 38 seconds.

with ASLR disabled it took 109 minutes and 55 seconds.

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