[ltp] How much performance improvement going from 32-bit to 64-bit linux?

[Micha Feigin]

On Thu, 17 Sep 2009 19:43:16 -0800
portsample <portsample@blepsias.net> wrote:

> 
> Hey all,
> 
> I've recently upgraded to a T60 running a Core 2 Duo T7600 Mobile
> Processor (2.33 ghz), lots of RAM and a 7200rpm HD. I am currently
> running openSuse 11.1, 32-bit.
> 
> I am thinking about installing 64-bit openSuse 11.2 when it is released
> in November.
> 
> Does anyone have any experience with moving from 32-bit linux OS to
> 64-bit? 
> 
> What kind of performance increase will I see? 
> 
> What kind of problems will I have?
> 
> Thanks. 
> 

If you are running no more than 2GB ram and/or heavily mathematical software
that makes heavy use of sse you will probably see somewhere between no to
negative improvement.

What 64bit gives you is (fast and easy) access to memory above the 2gb point
and double the amount of sse registers but at the cost of usually around 30%
more memory usage from software as pointers and long are 8 byte instead of 4
byte. This as a result causes bigger memory transfers and more cache misses.
Lastly, as processors still run 32bit instructions natively and not in
emulation mode, so 32bit instructions don't incur additional overhead, leads
to the point where on standard usage patterns you may actually lose performance.