AMD vs Intel memory managemement

Mon Jun 3 14:09:33 MST 2013

I have not run CentOS on my current system, but ununtu 13.04 ran like a
champ until i broke it. all 16 GB (2x8 set up as dual channel).

I can try to install Cent and see what it tells me. it may be that there is
a kernel param that is not lined up right.

On Mon, Jun 3, 2013 at 1:46 PM, Nathan England <nathan at nmecs.com> wrote:

> **
>
>
>
>
>
> Your explanation seems about right to me. The problem though, with a
> single processor with multiple cores, they are all using the same memory
> interconnect.
>
>
>
> While in theory, and quite possibly in true NUMA systems, this is a more
> efficient way to handle memory management with tasks assigned to a specific
> processor ( I would imagine this would be huge for VM hosts ) but as far as
> I know, there are no real world examples or tests that show this actually
> works any faster with multiple cores.
>
>
>
> But why does CentOS not register all of my memory? Why less than 3/4 of
> it? I have actually had my machine swap due to the work load where as if it
> had access to the other 3 GB of ram it would not have swapped!
>
>
>
> Maybe I should have gone with a single 8GB stick of ram instead of dual
> 4GB. Silly me!
>
>
>
> Nathan
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>
>
> On Monday, June 03, 2013 13:27:18 Nadim Hoque wrote:
>
> If i recall AMD started doing NUMA which each core gets a dedicated amount
> of memory that is tied to it. The plus side is that when the core needs
> something in its own memory region it does not need to put the request in
> the queue like in non-numa and gets it faster. The down side is if it needs
> data in a memory region that belongs to another core it will take longer
> since it essentially has to ask that core for that data. In non-numa
> architecture the entire memory space is allocated to all cores which means
> that each core can access memory with out asking another for data. The
> problem with this is that all memory requests is put in a queue and the
> core has to wait until the memory controller is able to process the
> request.  For many core and lot of memory systems you are mostly better off
> with NUMA. Correct me if I am wrong though.
>
>
>
> On Mon, Jun 3, 2013 at 7:25 AM, Stephen <cryptworks at gmail.com> wrote:
>
> Not really, Dual channel mode means you can read and write to both Banks
> of memory at the same time (aka Ganged). Single Channel means you treat all
> ram as a single bank reading and writing to one and then the other. think
> Raid 0 vs JBOD if that helps.
>
> I personally have had 0 issue with greater than 4 GB of ram in a machine
> with Linux and a 64 bit kernel. and i have worked with multiple
> distributions over the years back and forth.
>
> the main difference between Intel and AMD i have seen since the core i
> series CPUs were released is that AMD still has wicked fast memory
> performance but Intel wins most everything else.
>
> If you have multiple processors you will want to look for numa. This
> allows inter processor communication for ram access.
>
> It should not matter if you are running ganged or unchanged your is should
> see all ram installed with the exception of the PCI/pcie/chip set nibbling
> 100 to 700mb for doing its thing in consumer chipsets.
>
> On Mon, Jun 3, 2013 at 6:36 AM, keith smith <klsmith2020 at yahoo.com> wrote:
>
>
>
>
> I found this in an on-line discussion:
>
> Ganged = dual channel mode for ram. All cores get access to 100% of the
> ram.
>
> unganged = single channel. Each core gets access to a stick of ram.
>
> Is this correct?
>
>
> ------------------------
> Keith Smith
>
> --- On Mon, 6/3/13, Nathan England <nathan at nmecs.com> wrote:
>
>
> From: Nathan England <nathan at nmecs.com>
> Subject: Re: AMD vs Intel memory managemement
> To: "Main PLUG discussion list" <plug-discuss at lists.phxlinux.org>
> Date: Monday, June 3, 2013, 1:35 AM
>
>
>
>
>
>
>
> Yeah, it's a wonderful thing AMD calls "unganged" mode. I have 8 GB of ram
> in my server and the motherboard has enabled "unganged" mode to be more
> efficient. CentOS only recognizes 5.8 GB of ram and I cannot turn off
> unganged mode.
>
>
>
> I love it...
>
>
>
> </sarcasm>
>
>
>
>
> On Sunday, June 02, 2013 17:46:19 keith smith wrote:
>
>
>
>
> Hi,
>
> After that great thread on 32bit vs 64bit, I was wondering if it would be
> beneficial at this point to drill down to the CPU level : AMD vs Intel.
>
> We had a great thread a while ago the AMD CPU, however I do not think that
> thread covered memory management.
>
> I almost went for an AMD CPU this go around (I have a couple from prior
> purchases), however after hearing that AMD does some weird memory
> management at the core level, assigning memory by the bank to each core, I
> thought I would go with an Intel CPU.
>
> If I understand this correctly, It sounds like under some or most
> circumstances the server will lose a portion of the total memory because
> under AMD RAM is assigned at the core level and bank level.  I assume Intel
> uses memory as a pool.  Need memory just grab some until it is gone.
>
> Any thoughts on this?
>
> Thanks!
>
> ------------------------
> Keith Smith
>
>
>
> --
>
>
>
>
>
>
>
> Regards,
>
>
>
> Nathan England
>
>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> NME Computer Services http://www.nmecs.com
>
> Nathan England (nathan at nmecs.com)
>
> Systems Administration / Web Application Development
>
> Information Security Consulting
>
> (480) 559.9681
>
>
>
>
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> --
> A mouse trap, placed on top of your alarm clock, will prevent you from
> rolling over and going back to sleep after you hit the snooze button.
>
> Stephen
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>
>
> --
>
> Nadim Hoque
> Systems Support Analyst
> Engineering Technical Services
> Arizona State University
> Cell: 480-518-6235
>
>
>
> --
>
>
>
>
>
>
>
> Regards,
>
>
>
> Nathan England
>
>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> NME Computer Services http://www.nmecs.com
>
> Nathan England (nathan at nmecs.com)
>
> Systems Administration / Web Application Development
>
> Information Security Consulting
>
> (480) 559.9681
>
>
>
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> PLUG-discuss mailing list - PLUG-discuss at lists.phxlinux.org
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-- 
A mouse trap, placed on top of your alarm clock, will prevent you from
rolling over and going back to sleep after you hit the snooze button.

Stephen
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