On Mon, 16 Mar 2009, apostolos pantazis wrote:
Guys, we have a number of homegrown applications (C and even some
Fortran). Lots of Java of course much like everybody else these days.
I am counting on RPC being compatible. Lots of custom printing
configurations (I am assuming printing will not be an issue between
32/64). From what I am hearing it looks like I may want to get a 64
Bit backbone (server hardware/OS) but still run in compat mode for a
while (32 BIT binaries). I know this may sound dumb but any problems
with Java? I am expecting the path of least resistance on this item
but you never know so I am asking :)
I'm not supporting much java yet, so I may be off on this, but as I
understand things you typically end up running several JVMs on a single
box to take good advantage of multiple cores (and to allow you to isolate
different apps from each other)
if you are running things like this, you should have no problem sticking
with 32 bit userspace. you will be limited in how much ram you can
allocate to each JVM, but by running several you can make use of the large
amounts that you can fit in a mid-range box nowdays. don't forget to
'allocate' ram for use as a disk cache by the OS.
by going to a 64 bit kernel you let it take full advantage of the
hardware.
there's not as much difference between the 64 bit ans 32 bit codepaths as
there used to be (they are now merged into a single 'x86' architecture for
linux), but there are a lot of tricks that a 32 bit system needs to pull
to address more than 4G of address space (figure 1-2G of real ram), and
there are several known deadlock conditions that you can run into when you
use 32 bit systems with 8-16G of ram in them. nowdays my 'low-end' ($3k)
systems are getting 8g, and my 'high-end' ($5-8K++) systems are getting
64G on a fairly routine basis.
David Lang
On Mon, Mar 16, 2009 at 10:23 PM, <[email protected]> wrote:
On Tue, 17 Mar 2009, Brad Knowles wrote:
on 3/16/09 11:20 PM, [email protected] said:
It depends on what you're doing. Some applications have not yet been
ported to 64-bit, and may not run correctly on a machine that has a
64-bit kernel. Other applications may run better in 64-bit mode. You
need to know your specific application.
do you have any specific examples? the last usespace program that I ran
into with this sort of bug was the ipchains binary, and that was fixed
several years ago.
I've heard of no end of problems with precompiled binaries provided by
vendors for things like Flash, Nvidia drivers, etc....
using a 32 bit flash as a plugin to a 64 bit browser is an issue. that issue
ended up getting resolved by people figuring out that you could use
ndiswrapper to run flash (and several distros do this by default now). this
doesn't make flash stable (does anything??), but it does mean that when
flash locks up it doesn't crash the browser, so you can do a graceful exit
when you want to.
there is a 64 bit flash in alpha status right now. I'm running it on my
laptop and it crashes once in a while, taking the browser down with it. I'm
not sure it's a win, but I'm continuing to run it to be a beta-tester and
encourage Adobe to support linux better.
java brwser plugins are in a similar situation, but are not quite as bad.
Sun has a 64 bit java in beta. it's a but ugly to get setup as a plugin, but
seems far more stable.
as for nVidia, binary drivers are a nightmare in any case, they are distro
and kernel version specific, and they tie in directly to the kernel address
space. don't try to use them with any kernel they weren't directly tested
with (and this includes not using them with an distro kernel update if they
weren't made specificly for that update).
Admittedly, that's a more workstation-oriented issue as opposed to a
server problem, but it's certainly a valid class that may be of potential
concern. And anywhere else you've got a pre-compiled binary you have to deal
with, is a potential source of problems.
I'm not trying to say that you don't have valid concerns, but I have been
running 32 bit code on 64 bit kernels for quite a while (both server and
workstation), including in high-volume production settings (the vendor
hadn't gotten around to releasing a 64 bit version yet), and I have found
things to be very reliable.
if you are going to have problems, I would expect to see them in things that
try to muck directly with the kernel (CD burning software, userspace device
drivers, etc. things that are linux-only, and frequently version and/or
distro specific). applications that are portable across platforms give me no
problems, even demanding applications like databases
David Lang
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