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Old 05-06-2008, 03:29 PM
Marc Schiffbauer
 
Default 32bit or 64bit?

* Marek Podmaka schrieb am 06.05.08 um 16:55 Uhr:
> Hello all,
>
> I just yesterday learned that my Xeons are in fact 64bit, so I have
> few questions about it...
>
> 1) What is the performance gain between running 32bit and 64bit linux
> on 64bit capable CPU? I'm running Etch with apache+php+mysql. Is it
> worth upgrading?

For mysql it *might* be worth. How much RAM do these machines have?
If its less than 4GB its not worth upgrading. IMO its even better to
use x86 for those systems.

>
> 2) Performance is gained just by compiling the same source code into
> 64bit binary? Or are the main apps (apache/php/mysql) optimized in
> source code to benefit explicitly from 64bit?

Databases *might* perform a bit better because of 64bit integers they
can use.


>
> 2) Is it possible to run 64bit kernel, but 32bit
> application/libraries/everything? (So just recompiling kernel). If
> possible, is it better than 32bit kernel + 32bit apps?

Its possible. The advantage is that you could run 64bit apps in a
64bit chroot environment then for example.

>
> 3) Is it somehow possible to upgrade the 32bit debian into 64bit?
> Preferably with as little downtime as possible...

I guess not.

HTH

-Marc
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Old 05-06-2008, 03:38 PM
Matt Cuttler
 
Default 32bit or 64bit?

Marek Podmaka wrote:


> 2) Is it possible to run 64bit kernel, but 32bit
> application/libraries/everything? (So just recompiling kernel). If
> possible, is it better than 32bit kernel + 32bit apps?

Yes; in fact you don't have to do your own compilation; you can apt-get
install the linux-image-amd64 package -- on an otherwise 32-bit
(userspace) system. Providing, of course, your Intel CPU is 64-bit capable.

In general, I've found no reason to run the 64bit distribution on COTS
Intel/AMD servers, but I have had occasion to run the 64bit kernel (i.e.
servers with lots of RAM). But even that may be accomplished with
linux-image-686-bigmem instead.

-Matt Cuttler


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Old 05-06-2008, 03:55 PM
"Wojciech Ziniewicz"
 
Default 32bit or 64bit?

2008/5/6 Marc Schiffbauer <marc@schiffbauer.net>:

> For mysql it *might* be worth. How much RAM do these machines have?
> If its less than 4GB its not worth upgrading. IMO its even better to
> use x86 for those systems.
>

64bit processors are very very very rarely faster than 32bit processors.

moreover - depending whath application you run (based on processes or
threads etc..) it may affect how much RAM does your app take.
generally you have to have up to 30% ram more when running 64bit apps
on 64bit machine.

take a look here : http://www.phoronix.com/scan.php?page=article&item=616&num=3

and more detailed assembler-level changes here :
http://www.cs.cmu.edu/~fp/courses/15213-s06/misc/asm64-handout.pdf

and sample post aobut gettimeofday() and such things on 64bit here:
http://www.ussg.iu.edu/hypermail/linux/kernel/0702.0/0082.html

Summing up - 64bit is sometimes faster but almost always , your apps
will eat more RAM.

regards.







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Old 05-06-2008, 05:26 PM
Michael Loftis
 
Default 32bit or 64bit?

--On May 6, 2008 4:55:34 PM +0200 Marek Podmaka <marki@marki-online.net>
wrote:



Hello all,

I just yesterday learned that my Xeons are in fact 64bit, so I have
few questions about it...

1) What is the performance gain between running 32bit and 64bit linux
on 64bit capable CPU? I'm running Etch with apache+php+mysql. Is it
worth upgrading?


Probably none. What you gain mostly from an ISPs perspective is much
bigger memory support. For database servers this can be extremely
important. In 32bit you can have more than 4GB of memory (through PAE) but
each process can only have 2GB or 3GB. Also PAE is slower than directly
accessing additional memory because you are Paging memory in and out of a
window.



2) Performance is gained just by compiling the same source code into
64bit binary? Or are the main apps (apache/php/mysql) optimized in
source code to benefit explicitly from 64bit?


No, and in general, no.



2) Is it possible to run 64bit kernel, but 32bit
application/libraries/everything? (So just recompiling kernel). If
possible, is it better than 32bit kernel + 32bit apps?


Yes, amd64 variant of debian has 32bit libs so you can run 32bit based apps.


3) Is it somehow possible to upgrade the 32bit debian into 64bit?
Preferably with as little downtime as possible...


I don't know. Maybe? It's technically not an upgrade at all, but an
architecture change. Someone else on the list might know, but it's nothing
I've ever tried.




many thanks

--
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Old 05-06-2008, 11:26 PM
Craig Sanders
 
Default 32bit or 64bit?

On Tue, May 06, 2008 at 04:55:34PM +0200, Marek Podmaka wrote:
> Hello all,
>
> I just yesterday learned that my Xeons are in fact 64bit, so I have
> few questions about it...
>
> 1) What is the performance gain between running 32bit and 64bit linux
> on 64bit capable CPU? I'm running Etch with apache+php+mysql. Is it
> worth upgrading?

for most programs, not much. if any.

the main advantage is that each process can have direct access to ALL of
the memory in your system...whereas on a 32-bit kernel (even with PAE),
each process can access no more than (IIRC) 3GB.

the "cost" is that 64-bit apps use more memory than 32-bit apps. but see
my answer to your second point 2 :-) below, you can run 32-bit apps on a
64-bit kernel. you can even run a mix of 32 and 64 bit apps on a 64-bit
kernel. OTOH, i've been running 64 bit for over a year now and haven't
noticed or cared about any addition memory usage....but all my machines
have a minimum of 2GB if not 4GB or 8GB RAM. memory is very cheap. it's
easier and less hassle to just install more RAM than to care about it,
and more RAM is *always* better.


seriously memory-hungry apps (databases, huge number-crunching
computations, video editing, and others) will benefit. others, probably
not.

mysql would probably benefit if your db is large.

a multi-threaded apache may benefit. pre-forking probably not. if you're
running PHP, you're probably not running multi-threaded (anyone know if
php5 still buggy with MT? i've lost track).


ultimately, 32-bit will die....but i don't see that happening for many
years, probably decades. some current, production CPUs are still 32-bit
now, and even when it's no longer in use for general purpose computers,
32-bit CPUs will continue to be common in embedded devices.


> 2) Performance is gained just by compiling the same source code into
> 64bit binary? Or are the main apps (apache/php/mysql) optimized in
> source code to benefit explicitly from 64bit?

some will be, some won't. some will benefit from 64 bit, some wont.
depends on the app.


> 2) Is it possible to run 64bit kernel, but 32bit
> application/libraries/everything? (So just recompiling kernel). If
> possible, is it better than 32bit kernel + 32bit apps?

yes. you can run the debian i386 32-bit distribution with a kernel
compiled for amd64. I do that on some machines, and it works
flawlessly. i also run pure 64-bit on other machines and it also works
flawlessly. by "flawlessly", of course, i mean "no problems specifically
related to running 64-bit kernel or programs"...the usual range of bugs
still apply

if you are running a 64-bit amd64 kernel with the 32-bit i386
distribution, then you can also install some packages from the 64-bit
amd64 distribution. so you can run most things from 32-bit userland, and
install a few 64-bit packages (plus required lib64 libraries) that are
known to benefit from 64 bit.

for an existing system that you don't want to reformat and reinstall
from scratch, this is the best thing to do.


similarly, it's also possible to run the 64-bit distro with some
packages from the 32-bit distro. AFAIK, this is mostly done by
people who want to run a 32-bit web browser for compatibility with
some binary-only plugins. and, i guess, also on servers with 32-bit
binary-only proprietary stuff. you just need to install the required
lib32 libraries.


> 3) Is it somehow possible to upgrade the 32bit debian into 64bit?
> Preferably with as little downtime as possible...

no.

well, it depends.

if you just want 64-bit kernel and keep your 32-bit userland, then
it's just a matter of installing a 64 bit kernel. downtime is minimal -
however long it takes to reboot.


if you want to completely convert to the amd64 distro, then you have
to 1. backup, 2. reformat, 3. install from scratch, then 4. restore
your config and data files. IMO, not worth it unless you have some
particular need to do so (if you don't know for sure that you do, then
you almost certainly don't)...you can always convert to pure 64 bit next
time you replace/upgrade the machine.


craig

--
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BOFH excuse #73:

Daemons did it


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Old 05-07-2008, 07:57 AM
Matus UHLAR - fantomas
 
Default 32bit or 64bit?

> 2008/5/6 Marc Schiffbauer <marc@schiffbauer.net>:
> > For mysql it *might* be worth. How much RAM do these machines have?
> > If its less than 4GB its not worth upgrading. IMO its even better to
> > use x86 for those systems.

On 06.05.08 17:55, Wojciech Ziniewicz wrote:
> 64bit processors are very very very rarely faster than 32bit processors.

from what I've heard, there's a difference between Intel AMD processors here
- someone said that when AMD switches to 64bit, it speeds things up, while
Intel slows them down...

this information is quite old and I'd likt someone to confirm or disprove
it.

> moreover - depending whath application you run (based on processes or
> threads etc..) it may affect how much RAM does your app take.
> generally you have to have up to 30% ram more when running 64bit apps
> on 64bit machine.

mostly because all pointers use 64bit instead of 32bit.

> Summing up - 64bit is sometimes faster but almost always , your apps
> will eat more RAM.

--
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Old 05-07-2008, 09:01 AM
"Wojciech Ziniewicz"
 
Default 32bit or 64bit?

2008/5/7 Matus UHLAR - fantomas <uhlar@fantomas.sk>:
> from what I've heard, there's a difference between Intel AMD processors here
> - someone said that when AMD switches to 64bit, it speeds things up, while
> Intel slows them down...
>
> this information is quite old and I'd likt someone to confirm or disprove
> it.
>
yes - i've heard about it too . probably it was regarding amd pure
64bit processors and intel processors with emt64 (64bit emulation)
where obviously amd64bit was faster.


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Old 05-09-2008, 06:33 AM
Thomas Goirand
 
Default 32bit or 64bit?

Marek Podmaka wrote:
> Hello all,
>
> I just yesterday learned that my Xeons are in fact 64bit, so I have
> few questions about it...
>
> 1) What is the performance gain between running 32bit and 64bit linux
> on 64bit capable CPU? I'm running Etch with apache+php+mysql. Is it
> worth upgrading?

Hi,

I was quite surprised to see so many people saying that 64 bits goes at
the same speed, or is even slower. To what I could "feel", there is some
improvements.

64 bits arch have few hardware advantage:
1/ 8 general purposes registers instead of 4. That alone should justify
to use as much 64 bits binaries as you can.
2/ No more ugly memory pages that are slow to process, coming from an
old age, and really stupid IMHO.

Note that, if I'm not mistaking and as opposite to what I could read
here, this is ALSO an improvement when you have less than 4 GB of RAM
(eg: there is no more page fault interrupt in the processor).

> 2) Performance is gained just by compiling the same source code into
> 64bit binary? Or are the main apps (apache/php/mysql) optimized in
> source code to benefit explicitly from 64bit?
>
> 2) Is it possible to run 64bit kernel, but 32bit
> application/libraries/everything? (So just recompiling kernel). If
> possible, is it better than 32bit kernel + 32bit apps?

Sure it's possible, but not so wise, IMHO. I think it's best to always
run in 64 bits mode, and "apt-get install ia32-libs" to be able to run
binaries in 32 bits. Sure, it will take more memory. But hey, memory is
cheap these days...

Thomas


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Old 05-09-2008, 07:25 AM
Boris Pavlov
 
Default 32bit or 64bit?

Just my X cents: after moving to 64bit one of my mysql servers I'll
never go back to 32 bit. Call it whatever you wish.


And, about AMD ... it is pity. Not my words, but I do agree 1001% with
them: "AMD - an example how to destroy years of leadership".


I do not need 3 or 7 cores tomorrow, possibly working, I do need them
now, and please, don't blame Intel for doing their job better. I do not
need future technologies tomorrow.


These words are not a flame - I was a big AMD fan until couple of years ago.

edi.



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Old 05-22-2008, 07:36 AM
kj
 
Default 32bit or 64bit?

Craig Sanders wrote:

a multi-threaded apache may benefit. pre-forking probably not. if you're
running PHP, you're probably not running multi-threaded (anyone know if
php5 still buggy with MT? i've lost track).


I'm curious about this too.

Also, does this problem still exist in Etch 64bit:
http://kb.parallels.com/en/967

Having a 1024 limit made sense on hardware some years ago, but really,
today's monsters can cope with much much more.


--kj


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