AMD Athlon64 X2 Dual-core and 4GB

AMD Athlon64 X2 Dual-core and 4GB

[Vladimir Lazarenko]

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Hello,

Looking at the thread of Interl Dual-core and 4GB a sudden thought came 
to my mind: "Hey, I'm gonna upgrade my box to 4G next week too... Would 
it work?"

Thus, the question - would I be able to use whole 4G RAM with dual-core 
amd and kernel with SMP compiled for i686?

Thanks in advance!

Vladimir

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Re: AMD Athlon64 X2 Dual-core and 4GB

[Joel Jaeggli]

On Thu, 27 Oct 2005, Vladimir Lazarenko wrote:

> Hello,
>
> Looking at the thread of Interl Dual-core and 4GB a sudden thought came to my 
> mind: "Hey, I'm gonna upgrade my box to 4G next week too... Would it work?"
>
> Thus, the question - would I be able to use whole 4G RAM with dual-core amd 
> and kernel with SMP compiled for i686?

Yes but you would only be able to malloc 3GB per process. Go with the 
x86_64 kernel and that goes away. we have x86_x64's with 16GB of ram.

> Thanks in advance!
>
> Vladimir
>

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Re: AMD Athlon64 X2 Dual-core and 4GB

[Alejandro Bonilla]

On Thu, 27 Oct 2005 23:03:07 +0200, Vladimir Lazarenko wrote
> Hello,
> 
> Looking at the thread of Interl Dual-core and 4GB a sudden thought 
> came to my mind: "Hey, I'm gonna upgrade my box to 4G next week 
> too... Would it work?"
> 
> Thus, the question - would I be able to use whole 4G RAM with dual-
> core amd and kernel with SMP compiled for i686?

I think it's google time for you both.

Both Intel and AMD mention this problem all over the place, in Windows or Linux.

http://forums.amd.com/lofiversion/index.php/t51726.html

.Alejandro

> 
> Thanks in advance!
> 
> Vladimir


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Re: AMD Athlon64 X2 Dual-core and 4GB

[Eric W. Biederman]

Vladimir Lazarenko <vlad@lazarenko.net> writes:

> Hello,
>
> Looking at the thread of Interl Dual-core and 4GB a sudden thought came to my
> mind: "Hey, I'm gonna upgrade my box to 4G next week too... Would it work?"
>
> Thus, the question - would I be able to use whole 4G RAM with dual-core amd and
> kernel with SMP compiled for i686?

A Dual-core is a rev-E processor so the cpu has memory hoisting support,
so it will work if your BIOS implement it properly.

Eric

Re: AMD Athlon64 X2 Dual-core and 4GB

[thockin]

On Fri, Oct 28, 2005 at 09:30:51AM -0600, Eric W. Biederman wrote:
> > Thus, the question - would I be able to use whole 4G RAM with dual-core amd and
> > kernel with SMP compiled for i686?

Why would you use a dual core AMD in 32 bit mode?  Just build an x86_64
kernel.

If you want to use 4GB in 32 bit mode, you *need* remapping (or you lose
part of your memory).  Remapping means you have MORE than 4 GB of physical
address, which means you need PAE to use it at all.

Re: AMD Athlon64 X2 Dual-core and 4GB

[Eric W. Biederman]

thockin@hockin.org writes:

> On Fri, Oct 28, 2005 at 09:30:51AM -0600, Eric W. Biederman wrote:
>> > Thus, the question - would I be able to use whole 4G RAM with dual-core amd
> and
>> > kernel with SMP compiled for i686?
>
> Why would you use a dual core AMD in 32 bit mode?  Just build an x86_64
> kernel.
>
> If you want to use 4GB in 32 bit mode, you *need* remapping (or you lose
> part of your memory).  Remapping means you have MORE than 4 GB of physical
> address, which means you need PAE to use it at all.

Yes, and PAE works fine with a 32bit kernel.  I agree it is a silly
configuration and a 64bit kernel would use the memory more
efficiently.  My basic point was that a dual-core is a recent enough
processor from AMD that it supports memory remapping.  So with a
correct BIOS there should be no problems. 

Eric

Re: AMD Athlon64 X2 Dual-core and 4GB

[thockin]

On Fri, Oct 28, 2005 at 10:13:46AM -0600, Eric W. Biederman wrote:
> > If you want to use 4GB in 32 bit mode, you *need* remapping (or you lose
> > part of your memory).  Remapping means you have MORE than 4 GB of physical
> > address, which means you need PAE to use it at all.
> 
> Yes, and PAE works fine with a 32bit kernel.  I agree it is a silly
> configuration and a 64bit kernel would use the memory more
> efficiently.  My basic point was that a dual-core is a recent enough
> processor from AMD that it supports memory remapping.  So with a
> correct BIOS there should be no problems. 

Earlier Opterons had remapping, too, just at the chip-select level.  Even
with remapping, the memory that gets remapped gets mapped above 4 GB, so a
32 bit kernel still needs PAE to address it.

Re: AMD Athlon64 X2 Dual-core and 4GB

[Vladimir Lazarenko]

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>>>If you want to use 4GB in 32 bit mode, you *need* remapping (or you lose
>>>part of your memory).  Remapping means you have MORE than 4 GB of physical
>>>address, which means you need PAE to use it at all.
>>
>>Yes, and PAE works fine with a 32bit kernel.  I agree it is a silly
>>configuration and a 64bit kernel would use the memory more
>>efficiently.  My basic point was that a dual-core is a recent enough
>>processor from AMD that it supports memory remapping.  So with a
>>correct BIOS there should be no problems. 
> 
> 
> Earlier Opterons had remapping, too, just at the chip-select level.  Even
> with remapping, the memory that gets remapped gets mapped above 4 GB, so a
> 32 bit kernel still needs PAE to address it.

Well, my BIOS had 2 types of re-mapping, H/W and S/W, i enabled H/W 
remapping, compiled kernel with 64G HIGHMEM, and voila:

vlad@anarxi:~$ free
              total       used       free     shared    buffers     cached
Mem:       4151876    2972968    1178908          0     179008     679016
-/+ buffers/cache:    2114944    2036932


Thanks everyone!

Vladimir

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Re: AMD Athlon64 X2 Dual-core and 4GB

[Vladimir Lazarenko]

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>>>Thus, the question - would I be able to use whole 4G RAM with dual-core amd and
>>>kernel with SMP compiled for i686?
> 
> 
> Why would you use a dual core AMD in 32 bit mode?  Just build an x86_64
> kernel.
> 
> If you want to use 4GB in 32 bit mode, you *need* remapping (or you lose
> part of your memory).  Remapping means you have MORE than 4 GB of physical
> address, which means you need PAE to use it at all.

Because I find my distribution's 64-bit release reasonably unstable yet? :)

Or can I somehow build an x86_64 kernel and keep using 32-bit libc?

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Re: AMD Athlon64 X2 Dual-core and 4GB

[Eric W. Biederman]

Vladimir Lazarenko <vlad@lazarenko.net> writes:

>>>>Thus, the question - would I be able to use whole 4G RAM with dual-core amd
> and
>>>>kernel with SMP compiled for i686?
>> Why would you use a dual core AMD in 32 bit mode?  Just build an x86_64
>> kernel.
>> If you want to use 4GB in 32 bit mode, you *need* remapping (or you lose
>> part of your memory).  Remapping means you have MORE than 4 GB of physical
>> address, which means you need PAE to use it at all.
>
> Because I find my distribution's 64-bit release reasonably unstable yet? :)
>
> Or can I somehow build an x86_64 kernel and keep using 32-bit libc?

Building a x86_64 kernel is a bit of a trick on a 32bit distro.  
You need an appropriate version of gcc, and binutils.  But it runs
fine.

Eric

Re: AMD Athlon64 X2 Dual-core and 4GB

[Miquel van Smoorenburg]

In article <m11x25bn3j.fsf@ebiederm.dsl.xmission.com>,
Eric W. Biederman <ebiederm@xmission.com> wrote:
>Vladimir Lazarenko <vlad@lazarenko.net> writes:
>
>>>>>Thus, the question - would I be able to use whole 4G RAM with dual-core amd
>> and
>>>>>kernel with SMP compiled for i686?
>>> Why would you use a dual core AMD in 32 bit mode?  Just build an x86_64
>>> kernel.
>>> If you want to use 4GB in 32 bit mode, you *need* remapping (or you lose
>>> part of your memory).  Remapping means you have MORE than 4 GB of physical
>>> address, which means you need PAE to use it at all.
>>
>> Because I find my distribution's 64-bit release reasonably unstable yet? :)
>>
>> Or can I somehow build an x86_64 kernel and keep using 32-bit libc?
>
>Building a x86_64 kernel is a bit of a trick on a 32bit distro.  
>You need an appropriate version of gcc, and binutils.  But it runs
>fine.

I installed the 64 bit version of my distro on a small partition,
the 32 bit version on a larger partition. Then I compiled a kernel
on the 64 bit system, and installed it on the 32 bit partition.

Now I boot a 64 bit kernel for the 32 bit userland, and mount the
64-bit distribution partition under /amd64 - if I need to do
anything in 64 bit userland (like compile a new kernel) I just
chroot /amd64

Even the 64-bit binary nvidia kernel driver works fine with
a 32-bit X in userland.

Mike.

Re: AMD Athlon64 X2 Dual-core and 4GB

[Vladimir Lazarenko]

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>>Hello,
>>
>>Looking at the thread of Interl Dual-core and 4GB a sudden thought came to my
>>mind: "Hey, I'm gonna upgrade my box to 4G next week too... Would it work?"
>>
>>Thus, the question - would I be able to use whole 4G RAM with dual-core amd and
>>kernel with SMP compiled for i686?
> 
> A Dual-core is a rev-E processor so the cpu has memory hoisting support,
> so it will work if your BIOS implement it properly.
> 
> Eric

Thank you!

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