[ale] OT: 64 bit laptops

[Greg]

Ray:
thanks for the pointer to the aurora linux project.  I am in search of an OS
for my Blade 100.  It looks more and more like Slowlaris 9, as I want it for
mult-media stuff.

from the Aurora Linux project:

The whole 32bit vs 64bit issue
    Okay so you wonder why all the programs are currently built as 32bit
code not 64bit while only the kernel is 64? The answer is fairly complex:
    The Price of 64 bit: The cost of using 64bit operations throughout is
huge. Unless a number is bigger than 4294967296, the size of a 32 bit binary
number, most of the data is unused. This translates into effectively WASTING
half you main memory, memory bandwidth to the CPU and the CPU cache. This is
a huge performance hit.
    The Payoff of 64 bit: Well there are two actually: The first is that a
64bit CPU will usually be able to perform 64bit math and logic calculations
very quickly compared to a 32bit processor that will have to use software
fixes. Note this is mitigated by the fact many 32bit processors can do multi
register operations quickly. However as we have discussed above how many
times do you actually need 64 bit maths? That said if you have to use big
maths a native 64 bit arch is going to be fast.
    The second is more subtle and of far more import: with a 64 bit pointer
you can address more than 4GB of RAM. Note that there are hardware hacks to
allow a 32 bit x86 system to use more than 4 gigs but they require operating
system support and are very nasty and costly in performance terms. This HUGE
address space allows extremely large applications such as databases (4GB
isn't actually that large these days) to exist efficiently.
    Auroras Implementation: Aurora linux currently only supports a 32 bit
userland. This means the kernel exists in 64 bit space allowing it to use
more than 4GB of memory. Programs however are limited to 4GB of memory per
thread or program (e.g. 2 programs could use 8GB total). Work is currently
being done to bring a 64 bit userland into useability. As you can imagine
this is real in depth programming.

Greg


> -----Original Message-----
> From: ale-bounces at ale.org [mailto:ale-bounces at ale.org]On Behalf Of Ray
> Knight
> Sent: Saturday, November 08, 2003 5:46 PM
> To: Atlanta Linux Enthusiasts
> Subject: RE: [ale] OT: 64 bit laptops
>
>
> On Fri, 2003-11-07 at 00:54, Greg wrote:
> > 64 bits only is better than 32 in some respects - high end
> > graphics,modeling,multimedia, (perhaps mathematics) and huge
> databases.  I
> > have a UltraSPARC-IIe (64-bit SPARCv9 processor) and it drags
> on Solaris, is
> > ok on OpenBSD but the word from others is that they still get
> better mileage
> > on 32 bit architectures.  Or as one person advised me "64-bit
> applications
> > tend to be a tad bit slower than their 32-bit counterparts so
> even though
> > I'm running a 64-bit SPARCv9 kernel, I still compile those apps
> as 32-bit
> > programs using the Sun compilers and optimize the heck out of
> them."  As far
> > as the reports about the new Macs - who knows.  So much crap
> has been done
> > in the name of "benchmarks" that I am truly skeptical of just about
> > everything - especially if comparing 2 different systems (each should be
> > optimized by an expert in that system to really get a good comparison).
> >
> > Greg
> >
> You are correct.  Run your kernel 64bit and compile most apps at 32bit.
> Compile for 64bit only for those applications where memory usage or data
> access really needs the 64bit pointers (we're mostly talking specialized
> applications like James III mentioned earlier).
>
> I'm not familiar with all the 64 bit Linux distros, but the Aurora Linux
> distribution has most applications compiled 32bit, but uses a 64bit
> kernel for the UltraSparcs.
>
> Ray
>
>
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