Re: 64-bit vs 32-bit userspace/kernel benchmark? Was: Athlon 64 X2cpuinfooddities

[Jeffrey Hundstad]

David Lang wrote:

> On Tue, 10 Jan 2006, Jeffrey Hundstad wrote:
>
> > > On 1/10/06, Andi Kleen <ak@xxxxxxx> wrote:
> > >
> > > > On Tuesday 10 January 2006 03:12, Jesper Juhl wrote:
> > ...
> >
> > > > Ah - how legacy.
> > > Yeah, but since my distro of choice is 32bit only and I don't much
> > > feel like porting it myself or using an unofficial port (slamd64) I'm
> > > sticking with a 32bit userspace. And as long as userspace is pure
> > > 32bit there doesn't seem to be much point in building a 64bit kernel.
> > > And I only have 2GB of RAM, so I don't have a use for the larger 64bit
> > > address space.
> > > I also don't run any apps that do a lot of math on >32bit numbers, so
> > > there's not much gain there either.
> > > I guess I would bennefit from the extra GPR's, but then I would at the
> > > same time loose a bit by all pointers being 64bit - both lose some
> > > disk space due to larger binaries and I'd have increased memory use
> > > and less efficient L1/L2 cache use.
> > >
> > > I don't think there would actually be much gain for me in switching to
> > > a 64bit kernel with a 64bit userspace atm.
> > > But if I'm wrong I'd of course love to hear about it :)
> >
> > Has anyone done any actual benchmark tests that show 64-bit vs 32-bit 
> > environments/distributions with Athlon64 processors.  If so, I love 
> > to see the results.  I too elected to stick with 32-bit, using the 
> > same reasoning/guessing above.
>
>
> remember that benchmarks are all dependant on your workload, but on 
> some of my workloads (lots of fork-based network services) I've seen a 
> 50%+ increase by switching from a 32 bit to 64 bit kernel with 32 bit 
> userspace, and a further 50%+ increase by switching to a 64 bit 
> userspace.

Thanks for your response.  I'm prob. being stupid here... but does 
"increase" here mean faster or slower?

> remember that on amd64 systems 64 bit programs have access to twice as 
> many registers as 32 bit programs. This can be more of a win then the 
> extra pointer size is a loss.


If you've done other "standard" type of benchmarks between the two 
please post your results.  Also, is there a big hit by using a nearly 
pure 32-bit environment + the rare 64-bit program when needed?

--
Jeffrey Hundstad

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