How about NUMA?

[lee-25]

Hi,

under what circumstances are you supposed to turn on NUMA support in
the kernel settings? I've googled about that and learned what NUMA is
about while trying to answer the question wheather I should enable it
in my kernel or not. But I couldn't find the answer I was looking for.

Do Intel DualCores (E8400) support NUMA? Do you need special hardware,
like a special mainboard supporting NUMA, to benefit from this
feature? Do these CPUs support NUMA? It seems to me that leaving it
disabled is better in my case, and the kernel help also says that it's
probably better not to enable it if you don't have more than two
CPUs/cores.

Now if I had a quad core CPU instead, would I better enable NUMA? Or
if I had an AMD instead of Intel, would I turn it on? Or should I
leave it turned on?


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[Masood-4]

On Thu, Jul 9, 2009 at 1:49 PM, lee <lee@...> wrote:

Hi,

under what circumstances are you supposed to turn on NUMA support in
the kernel settings? I've googled about that and learned what NUMA is
about while trying to answer the question wheather I should enable it
in my kernel or not. But I couldn't find the answer I was looking for.

Do Intel DualCores (E8400) support NUMA? Do you need special hardware,
like a special mainboard supporting NUMA, to benefit from this
feature? Do these CPUs support NUMA? It seems to me that leaving it
disabled is better in my case, and the kernel help also says that it's
probably better not to enable it if you don't have more than two
CPUs/cores.

Now if I had a quad core CPU instead, would I better enable NUMA? Or
if I had an AMD instead of Intel, would I turn it on? Or should I
leave it turned on?

I think NUMA only makes sense in a CPU architecture where each group of processor cores have their own memory controller such as multi-socket AMD K8 or K10 (Opteron) and Intel Nehalem-based Xeons.


Regards,
Masood 

 

[Micha Feigin]

On Wed, 8 Jul 2009 21:49:00 -0600
lee <lee@...> wrote:

> Hi,
>
> under what circumstances are you supposed to turn on NUMA support in
> the kernel settings? I've googled about that and learned what NUMA is
> about while trying to answer the question wheather I should enable it
> in my kernel or not. But I couldn't find the answer I was looking for.
>
> Do Intel DualCores (E8400) support NUMA? Do you need special hardware,
> like a special mainboard supporting NUMA, to benefit from this
> feature? Do these CPUs support NUMA? It seems to me that leaving it
> disabled is better in my case, and the kernel help also says that it's
> probably better not to enable it if you don't have more than two
> CPUs/cores.
>
> Now if I had a quad core CPU instead, would I better enable NUMA? Or
> if I had an AMD instead of Intel, would I turn it on? Or should I
> leave it turned on?
>
>

A good first answer is that if you don't know what NUMA is then you don't need
it. If you want a more precise answer what NUMA is:

NUMA = non uniform memory access. It means that each cpu connects directly to
it's local memory and slowly (via some communication channel) to other memory.
The closest you would get with a desktop box (which I don't think is possible
yet) would be with a dual CPU core i7 (note, dual cpu, not dual core), since
corei7 has it's own memory controller. Core 2 duo connects via the north side
bus and thus even with two CPUs they still connect to the same memory via the
north side bus. If you have a multi CPU opetron system they also are NUMA
systems.


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[Ron Johnson]

On 2009-07-08 22:49, lee wrote:
> Hi,
>
> under what circumstances are you supposed to turn on NUMA support in
> the kernel settings? I've googled about that and learned what NUMA is
> about while trying to answer the question wheather I should enable it
> in my kernel or not. But I couldn't find the answer I was looking for.
>
> Do Intel DualCores (E8400) support NUMA?

No.  All cores access the same RAM over the same paths.

>                                           Do you need special hardware,
> like a special mainboard supporting NUMA, to benefit from this
> feature?

Yes.  Really expensive server-oriented multi-*socket* boards with
DIMM slots for each CPU socket.

>          Do these CPUs support NUMA? It seems to me that leaving it
> disabled is better in my case, and the kernel help also says that it's
> probably better not to enable it if you don't have more than two
> CPUs/cores.
>
> Now if I had a quad core CPU instead, would I better enable NUMA? Or
> if I had an AMD instead of Intel, would I turn it on? Or should I
> leave it turned on?

You still only have 1 CPU chip, so NUMA is irrelevant.

--
Scooty Puff, Sr
The Doom-Bringer


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[lee-25]

At Sun, 19 Jul 2009 20:11:03 -0500,
Ron Johnson wrote:

>
> On 2009-07-08 22:49, lee wrote:
> > Hi,
> >
> > under what circumstances are you supposed to turn on NUMA support in
> > the kernel settings?
>
> Really expensive server-oriented multi-*socket* boards with
> DIMM slots for each CPU socket.
>
> You still only have 1 CPU chip, so NUMA is irrelevant.

Thanks! Interestingly, you can turn it on nonetheless, and it works
...


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[Ron Johnson]

On 2009-07-20 00:08, lee wrote:

> At Sun, 19 Jul 2009 20:11:03 -0500,
> Ron Johnson wrote:
>> On 2009-07-08 22:49, lee wrote:
>>> Hi,
>>>
>>> under what circumstances are you supposed to turn on NUMA support in
>>> the kernel settings?
>> Really expensive server-oriented multi-*socket* boards with
>> DIMM slots for each CPU socket.
>>
>> You still only have 1 CPU chip, so NUMA is irrelevant.
>
> Thanks! Interestingly, you can turn it on nonetheless, and it works

That's because the kernel doesn't just use stuff simply because you
compile it in.  Search thru dmesg and you might see something
enlightening regarding NUMA.

--
Scooty Puff, Sr
The Doom-Bringer


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[lee-25]

On Mon, Jul 20, 2009 at 12:33:10AM -0500, Ron Johnson wrote:
>>> You still only have 1 CPU chip, so NUMA is irrelevant.
>>
>> Thanks! Interestingly, you can turn it on nonetheless, and it works
>
> That's because the kernel doesn't just use stuff simply because you  
> compile it in.  Search thru dmesg and you might see something  
> enlightening regarding NUMA.

Well, I haven't compiled it in anymore, but afair it was saying
something about faking a NUMA node.


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