Am I 32-bit, or 64-bit?

[Jerry Feldman]

On 04/05/2012 02:39 PM, Michael ODonnell wrote:
>> In the meantime...  is there any possible downside of having
>> a 64-bit kernel in a 32-bit userspace?  Everything -- drivers,
>> camera, apps -- seems just ducky.
> I've seen instances where 32bit apps and libraries disagreed
> with some 64bit drivers about the layout of the data structures
> that get passed back and forth (earlier versions of the FireWire
> driver versus libraw1394 come to mind) but in general, stuff
> should Just Work.  The 32bit binaries execute natively (ie.
> no emulation or translation overhead) and I think by now most
> kernel code has been taught to do the right thing when it
> sees that the current process is a 32bit binary.  One upside
> is that the 32bit processes are able to address an extra Gb
> of memory since the kernel no longer claims the top 1/4 of
> their address space...
I have seen that in 64-bit Linux, 32-bit processes tend to execute a bit
faster. I've seen a number of cases where 32-bit apps run faster than
their 64-bit version, but I've also seen 64-bit apps run faster than
their 32-bit versions. In any case Linux has been 64-bit since 1995 when
it was ported to the Digital Alpha chip, and Linux ported very easily to
the AMD 64 architecture when it came out. For the most part I have seen
no reason for running a 32-bit OS on a 64-bit chip. Just having the
extra 4 registers and linear memory give that extra speed advantage.
And, as you mention, 32-bit apps do run natively.  The disadvantage is
that you need both 64-bit and 32-bit libraries.

-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
PGP key id:3BC1EB90 
PGP Key fingerprint: 49E2 C52A FC5A A31F 8D66  C0AF 7CEA 30FC 3BC1 EB90


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