On Nov 12, 2007 11:37 AM, Sam Mason <sam@samason.me.uk> wrote:
> On Mon, Nov 12, 2007 at 11:31:59AM -0600, Scott Marlowe wrote:
> > On Nov 12, 2007 11:29 AM, Sam Mason <sam@samason.me.uk> wrote:
> > > You don't need a 32bit kernel to support 8GB of memory should you? As
> > > long as the kernel supports PAE that should be enough to make use of it.
> > > You only need a 64bit address space when each process wants to see more
> > > than ~3GB of RAM.
> >
> > There's a performance hit for using PAE. Not sure what it is, but I
> > recall it being the in the 5 to 10% range.
>
> And what's the performance hit of using native 64bit code? I'd guess
> similar, moving twice as much data around with each pointer has got to
> affect things.
That's not been my experience. It's not like everything you do
requires 64 bits to be moved where in 32 bit code only 32 were moved.
The performance gain of the 64 bit machine doing 64 bit operations
over the 32 bit machine doing them (i.e. floating point etc...) is so
much more that it more than makes up for the overhead of running in 64
bit mode.