F 15. 64 bit versus 32 bit.

[Bill Davidsen]

Alan Cox wrote:
>> Also, the ABI is much better, and this may be almost as significant.
>>
>>> Unfortunately that biggest gain only occurs if the program logic is such that
>>> registers run out often.
>>
>> Which, in the case of gcc-generated code, is most of the time.  gcc
>> was originally written for, and still works best with, a machine with
>> 16 or more general-purpose registers.  32- bit x86 only has five or
>> six registers to play with, and this just isn't enough for good code
>> generation.  I don't think that Java has it very much easier.
>
> The overall performance difference seems to be about 20% these days
> although of course very workload dependant. A 32bit kernel in particular
> really starts to hurt above 1GB RAM (actually about 900MB) and once you
> get towards 4GB the 32bit option becomes a complete waste.
>
You see things I don't. Running mail and news servers on identical hardware with 
12GB RAM I see about 4% difference in articles/sec. This is a serious but not 
extreme load, so it really is working a little faster in x86_64, but not 20%. If 
you mean 20% on some CPU bound number cruncher, that might be true, I no longer 
run loads like that for money, and haven't for years out of curiousity.

> KVM in some ways makes the choice easier. If you are running lots of
> guests then its often a very good idea that your main desktop environment
> is itself a guest - for security and convenience reasons. That makes it
> easy to have a 32bit guest around, or even keep a 32bit 'internet' guest
> just for browsing etc and to keep anything of value and the internet
> further apart from each other.
>
> [Also of course means you can have several guests some using tunnels if
>   you are paranoid about the black helicopters ;)]
>
You mean booting an encrypted disk with LUKS from an encrypted device created in 
qemu-img? I do have some interesting clients... And I do run my desktop in a VM, 
WFM.

-- 
Bill Davidsen <davidsen at tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot