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Subject: Re: FOR loops performance - 32bit vs 64 bit Matlab
Date: Mon, 13 Oct 2008 00:35:03 +0000 (UTC)
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Rune Allnor <allnor@tele.ntnu.no> wrote in message 
> 
> I agree with your sentiments, but I interpret the OPs post
> such that the same code runs in 17 seconds on the 32-bit
> computer and in 370 seconds on the 64-bit computer.
> 
> If any of the arguments you mention were valid, they ought to
> impact the performance on the 32 bit system as well, not only
> on the 64-bit system.
> 
> Seems to me there is a bug in the 64-bit version.
> 
> Rune

I can concur with this from results I have seen. I ran the following tests...
XP SP2 (32-bit) 2.4GHz core 2 Duo with r2007b 32-bit
Win2k3 (64-bit) 2x3GHz Xeon 5450 Quad Core with r2007b 32-bit HP blade.
Vista Business (64-bit) 1x3GHz Xeon Quad Core with r2007b 64-bit HP xw8600 workstation

The Desktop had 3GB memory, the server 16GB and Workstation 8GB. 
The 64-bit blade server running 32-bit Matlab (i.e. it's emulating a 32-bit env) gave a 25% performance increase over the desktop. However the all 64-bit workstation was, on average, around 60-70% slower than the desktop including running Matlab's own Bench functionality. 
I realise we're not comparing apples with apples here but for a 3GHz quad core Xeon workstation to underperform a 2.4GHz dual core desktop is some difference and is the direct 32-bit to 64-bit comparison. The workstation is also running faster memory and has a faster FSB.
I cannot believe this performance can be just down to the OS (it's too easy to point the finger at Vista) and believe that it may be the case that 32-bit Matlab is better optimised than it's 64-bit version.