F 15. 64 bit versus 32 bit.

[Gilboa Davara]

On Tue, 2011-05-24 at 11:27 -0400, Bill Davidsen wrote:
> Rahul Sundaram wrote:
> > On 05/24/2011 08:19 PM, Nat Gross wrote:
> >> Planning to install Fedora 15 on a new partition dual boot win 7.
> >> Hardware AMD 1090 (6 core) with 8 gig ram.
> >> Doing Java programming and plan to use KVM machines with Fedora as the host os.
> >> Of course regular stuff on the web including videos, etc.
> >>
> >> So, the question is. Is it still advisable to go 32 bit due to
> >> stability (say Flash), or can I gain performance and have 99%
> >> stability with 64 bit F 15?
> >
> > Virtualization certainly benefits a lot from x86_64 to the point that
> > RHEL6 only supports it on that architecture.  I would recommend going
> > with x86_64 for your use cases
> >
> What? Are you saying that KVM support is out of the PAE 32bit kernel? Because 
> libvirt, virt-manager, etc, are definitely shown as available packages. As far 
> as limitations and performance go, unless you have applications which push the 
> 4GB memory limit of PAE, you will be essentially the same in either case, but 
> will have a harder time finding third party applications for 64 bit.

What prevents you from installing 32bit 3'rd party applications (such as
flash) on x86_64?
Multi-lib is no longer an issue - at least not since Fedora 5-6.

> I have a pair of systems, i7-950, 12GB RAM, 4x1TB RAID5, doing VM hosting. One 
> is fc13 i686, one is fc13 x86_64. There is no obvious performance difference, 
> the only benefit of x86_54 is that I can run a 64 bit guest for testing.

PAE does have it's own performance penalties. (At least in my
experience, certain use-case show >10% performance hit)
As a VM server, running x86_64 guest and/or guests with >4GB RAM is an
issue.
... Plus, certain application (even ones that don't require >3GB RAM)
can use the extra GP registers and show a 10-100% performance
difference. YMMV.

> So: don't expect a big performance gain from 64 bit, unless you run some huge 
> app you would not be likely to see it. Don't expect stability problems, I'm not 
> sure that has ever lived up to the hype, the base OS seems fine, and has since 
> fc6, when I first tried 64 bit. DO expect more effort in finding 3rd party apps, 
> and occasionally some stability problems in that area (the latest 64 bit version 
> of vlc locks up in 64 bit, for example).

VLC is rock solid on my machines.
... In general, my advice is rather the opposite:
Unless you're severely limited by memory (<2GB), disk-space (mutli-lib)
or bandwidth (multi-lib again), x86_64 is your best bet.

> Don't expect to see a big difference whichever way you go, it depends on your 
> desire for 3rd party apps to some extent.

I fully agree.
Again, at least in the certain applications that I use, the added GP
registers do wonders in x86_64.

- Gilboa