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From: Aaron Toponce on 12 May 2010 17:40
On 5/12/2010 2:53 PM, Stefan Monnier wrote:
> I'd go with an i386 install unless you have more than 3GB of RAM, in
> which case I'd go with an amd64 install (or an i386 with a 686-bigmem
> kernel).

The 64-bit vs 32-bit argument is multi-faceted. It gets much deeper than
just addressing more than 3GB of RAM:

* twice the transfer width on the bus
* no memory split issues
* increased virtual address space
* more breathing room for mmap()'d files
* deeper nested system calls with increased stability
* certain applications and operations will execute faster

If you have the hardware, you should definitely be running a 64-bit
operating system, even if you don't have 4GB+ of RAM.

--
. O . O . O . . O O . . . O .
. . O . O O O . O . O O . . O
O O O . O . . O O O O . O O O

From: Aioanei Rares on 12 May 2010 18:30
On 05/13/2010 12:31 AM, Aaron Toponce wrote:
> On 5/12/2010 2:53 PM, Stefan Monnier wrote:
>
>> I'd go with an i386 install unless you have more than 3GB of RAM, in
>> which case I'd go with an amd64 install (or an i386 with a 686-bigmem
>> kernel).
>>
> The 64-bit vs 32-bit argument is multi-faceted. It gets much deeper than
> just addressing more than 3GB of RAM:
>
> * twice the transfer width on the bus
> * no memory split issues
> * increased virtual address space
> * more breathing room for mmap()'d files
> * deeper nested system calls with increased stability
> * certain applications and operations will execute faster
>
> If you have the hardware, you should definitely be running a 64-bit
> operating system, even if you don't have 4GB+ of RAM.
>
>
+1


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From: deloptes on 12 May 2010 18:40
Aaron Toponce wrote:

>
> If you have the hardware, you should definitely be running a 64-bit
> operating system, even if you don't have 4GB+ of RAM.
>

+1


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From: Stefan Monnier on 12 May 2010 21:10
> The 64-bit vs 32-bit argument is multi-faceted. It gets much deeper than
> just addressing more than 3GB of RAM:
> * twice the transfer width on the bus

Nope, no difference on the bus. Most accesses will be
cache-line-sized anyway at that level.

> * no memory split issues

For <=3GB systems, that makes no difference. And as someone running
a bigmem kernel on a 4GB system, I can say that even for other systems,
it's not necessarily relevant.

> * increased virtual address space

Right. Unlikely he'll ever notice it.

> * more breathing room for mmap()'d files

Again, unlikely he'll ever notice it (otherwise he wouldn't have asked).

> * deeper nested system calls with increased stability

I see no evidence of increased stability and have no idea what you want
to say with "deeper nested system calls".

> * certain applications and operations will execute faster

Yup. And others will be slower since you'll have to move around more
data (up to twice as much if your data is made up mostly of pointers),
which means that the apparent cache and RAM size will end up
being reduced.

> If you have the hardware, you should definitely be running a 64-bit
> operating system, even if you don't have 4GB+ of RAM.

If you have to ask, you probably won't notice any difference
either way.


Stefan


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From: Aaron Toponce on 12 May 2010 23:50
On 05/12/2010 07:03 PM, Stefan Monnier wrote:
>> The 64-bit vs 32-bit argument is multi-faceted. It gets much deeper than
>> just addressing more than 3GB of RAM:
>> * twice the transfer width on the bus
>
> Nope, no difference on the bus. Most accesses will be
> cache-line-sized anyway at that level.

You're kidding, right? You can push twice the data, which means faster
CPU to memory utilization for CPU intensive applications. Flash anyone?

>> * no memory split issues
>
> For <=3GB systems, that makes no difference. And as someone running
> a bigmem kernel on a 4GB system, I can say that even for other systems,
> it's not necessarily relevant.

It's very relevant. You must not have run into this issue much. 4:4
kernel splits are the best you can do on a 32-bit system, but it comes
at a performance cost. Splitting and performance are never an issue on
64-bit until you've reache 17 EB of RAM.

>> * increased virtual address space
>
> Right. Unlikely he'll ever notice it.

Whether he will or won't isn't the issue. I'm not discussing use cases,
I'm discussing the facts on why 64-bit is superior to 32-bit.

>> * more breathing room for mmap()'d files
>
> Again, unlikely he'll ever notice it (otherwise he wouldn't have asked).

See above.

>> * deeper nested system calls with increased stability
>
> I see no evidence of increased stability and have no idea what you want
> to say with "deeper nested system calls".

I'll give you an example. Use XFS on LVM, and export the mount over NFS.
The nested system calls in this scenario will cause a kernel oops on any
4K 32-bit kernel nearly every time (the default for Debian GNU/Linux,
Fedora, Ubuntu, openSUSE, etc). On a 64-bit kernel, because you have the
ability to make deeper nested system calls, you have stability in your
infrastructure. Something that couldn't be achieved with a 32-bit kernel.

>> * certain applications and operations will execute faster
>
> Yup. And others will be slower since you'll have to move around more
> data (up to twice as much if your data is made up mostly of pointers),
> which means that the apparent cache and RAM size will end up
> being reduced.

The same would be said for a 32-bit application implemented the same
way. Poor software development is hardly an argument against choosing a
CPU architecture.

>> If you have the hardware, you should definitely be running a 64-bit
>> operating system, even if you don't have 4GB+ of RAM.
>
> If you have to ask, you probably won't notice any difference
> either way.

To each their own. I for one want to get my money out of my hardware. If
you don't want a 64-bit system, then why did you pay for it?

--
. O . O . O . . O O . . . O .
. . O . O O O . O . O O . . O
O O O . O . . O O O O . O O O

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