Linux+CFD: is 64bit really a need?
Ok, I know this may sound trivial as many would immediately think "Of course! 64bit is way faster and more powerful than any 32bit".
Well, I'm most of the time a PCLinuxOS user, it's a very nice system, really fast compared to other 32bit systems (even other Linuxes, although I won't claim it's the fastest), and many complaint there's not a 64bit version. However, I came accross this the other days, and here I quote it:
1) 32bit Processor, 32bit Linux distro with PAE Kernel, software optimized for 32bit.
2) 64bit Processor, 32bit Linux distro with PAE Kernel, software optimized for 32bit.
3) 64bit Processor, 64bit Linux distro, software optimized for 64bit.
Let's suppose also that we are talking of a single desktop machine, budget irrestricted, to work at home, no clusters or similar high-end stations.
Which of these options would have the best performance? Which one of these options would be the one with highest performance/cost ratio?
Naturally I omitted other conditions, so when answering feel free to asume the circumstances. If other UNIX based systems have the possibility of using a PAE Kernel, you can mention them, I simply mentioned Linux because it's what I best know (Windows doesn't have PAE, so don't bother in mentioning it :D).
In my experience, here are the limitations for 32bit PAE and related issues:
edit: I forgot about a personal work experience of 32 vs 64bit builds of OpenFOAM: OpenFOAM 1.7 motorBike - Run Times
This page shows some runtimes of a single CFD case using OpenFOAM 1.7.0 cross-compiled with mingw-w64 running in Windows 7 x64, both 32 and 64bit builds, versus 32 and 64bit Linux versions of OpenFOAM 1.6.0 (openSUSE 10.3 x86_64 to be exact)! In both platforms, the 64bit version is always considerably faster, and the 64bit version in Windows almost catches up with the 32bit version of OpenFOAM in Linux :rolleyes:
Ironically, both Windows and openSUSE were 64bit versions, but running 32bit applications in a 64bit OS shouldn't have a considerable performance hit.
edit 2: as for the rendering times in PCLinuxOS, the drivers for the graphics card also play a key part of rendering times!
Exactly the kind of answer I was looking for!:) Thanks, Bruno.
Unfortunately this puts and end to my supercheap but superpowerful future machine, I'll have no choice than spending a few more bucks. It's nice to see however that Linux even in 32bit performs better than Win (interesting the info on the PAEs BTW), so after all it's not a bad idea for low-level works. It happens that I'm putting together a Linux distro destinated to engineering students, and since 32bit is cheap for their budget (like me:rolleyes:) I'm building everything to be used in low-powered hardware (I'm simply installing, configuring and then remastering, nothing special). Salome and Saturne run pretty slick so far (1.2million cells, k-e steady state in 20 iterations, 4hs in a Sempron LE1100 with 2GB RAM... horrible output though, lol).
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