[ug-bosug] Nevada and x86 64bit CPU's : a few questions

[Ashwin Bhat]

How does one set the PAE flag in Solaris ?

On Feb 12, 2008 11:44 PM, Ananth Shrinivas <Ananth.Shrinivas at sun.com> wrote:

> Hi Manish,
>
> Answers to a few of your questions:
>
> > I am looking for an Opteron based box with 8GB of RAM ( Saw one good
> > configuration for around 25k )
> >
> > Since Nevada userland is 32bit, would it be able to address all of the
> > 8GB of RAM or like Windows XP , only the first 4GB will be used?
>
> Since the kernel is 64 bit, you will be able to access all of your 8GB.
> In fact even the 32 bit unix kernel can access the entire 8GB because of
> the x86 Physical Address Extensions (PAE) (See:
> http://www.x86.org/articles/2mpages/2mpages.htm). It doesn't matter if
> the app is 32 bit or 64 bit since the app is only concerned with its
> Virtual Address Space and both the 32 and 64 bit kernels can see all of
> your physical address space.
> > know Ubuntu 64bit can access and utilize all of my 8 gigs if needed (
> > But Ubuntu , like all 64 bit Linux distros has full 64bit userland).
> > I am confused because Nevada userland is 32 bit but the kernel is
> > 64bit ( on machines which have 64bit capable CPU's )
> >
> > Two more questions:
> > 1) How does this work? ( 64bit kernel and 32 bit userland; could some
> > explain in a little detail?)
> >
> > 2) Why does Nevada not ship with full 64bit userland?
> > I understand #2 would break binary compatibility for 32bit apps.
>
> Nevada userland has a mix of both 32 and 64 bit apps. Take sort for
> example:
>
> $ file /usr/bin/sort /usr/bin/i86/sort /usr/bin/amd64/sort
> /usr/bin/sort:  ELF 32-bit LSB executable 80386 Version 1 [FPU],
> dynamically linked, not stripped, no debugging information available
> /usr/bin/i86/sort:      ELF 32-bit LSB executable 80386 Version 1 [FPU],
> dynamically linked, not stripped, no debugging information available
> /usr/bin/amd64/sort:    ELF 64-bit LSB executable AMD64 Version 1 [SSE2
> SSE FXSR CMOV FPU], dynamically linked, not stripped, no debugging
> information available
>
> $ ls -li /usr/bin/sort
> 1763 -r-xr-xr-x 95 root bin 8048 Jan 13 07:26 /usr/bin/sort
>
> $ ls -li /usr/lib/isaexec
> 1763 -r-xr-xr-x 95 root bin 8048 Jan 13 07:26 /usr/lib/isaexec
>
> The /usr/bin/sort is a hard link to /usr/lib/isaexec which decides on
> the fly whether to execute the 32 bit (i86) version or the 64 bit
> (amd64) version.
>
> But beware, while things like HPC apps, Multimedia Software and
> Databases usually benefit from a 64 bit userland: In other cases with
> data type bloat, address alignment constraints and limited cache lines,
> it is not entirely uncommon for 64 bit apps to be slower than their 32
> bit counterparts.
>
> Cheers,
> Ananth
>
>


-- 
Regards
Ashwin Bhat K S
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