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xen-users
Re: [Xen-users] RE: [Xen-devel] Modular Xen
"Petersson, Mats" <Mats.Petersson@xxxxxxx> writes:
> Resent with xen-users list as recipient, rather than directly to Daniel.
>
>> -----Original Message-----
>> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
>> Daniel Stodden
>> Sent: 18 January 2007 15:38
>> To: Xen Developers
>> Subject: Re: [Xen-devel] Modular Xen
>>
>> On Mon, 2007-01-15 at 19:30 +0200, David Pilger wrote:
>> > It seems to me that Xen is full of stuff that aren't beneficial for
>> > everybody, this includes NUMA, ACM and other stuff that certain
>> > companies try to introduce...
>>
>> can anyone explain to me what the current numa-bashing is all about?
>> i'm running a lot of my stuff on 4-way opteron servers, these
>> system are
>> far from uncommon these days and certainly beyond a mere 'introduction
>> attempt'.
>>
>> are there any numbers regarding the code size/performance penalty on
>> systems limited to a single memory node? i'd really be interested.
>
> I think this is the wrong thread for this subject (the one titled SMP & NUMA
> something or other started by Emmanuel Ackaroy (excuse spelling) is the right
> one...).
>
> But to sumarize the discussion, I don't think anyone is denying the need to
> have Xen understand NUMA. However, there are plenty of reasons that NUMA
> won't necessarily give any noticable benefit for the typical Xen system - for
> example, the default configuration is that all guests run on ANY available
> CPU, which means that allocating it's memory on any particular CPU will be
> just as right (or wrong) as allocating it in a random or scattered fashion.
>
> I completely understand where Emmanuel is coming from when he is "negative"
> about the benefits of NUMA in a Xen system. There are places with concrete
> and obvious benefits, but there's also a great risk that things just run
> slower if it's implemented in the wrong way (or USED in the wrong way).
>
> So there's some need to research the subject before adding the features into
> the Xen kernel. [The same applies to the Linux kernel of course].
Just so I know, does XEN pass on the NUMA infos from the allocated
memory to the domU linux kernel?
Say I do have NUMA and 2 cpus and start a domU with 1G ram and 2
vcpus. Does it allocate 512MB per NUMA node and tell linux that?
And do vcpus stay mapped to the same real cpu in case cpus == cpus or
do they randomly switch (making numa optimizations impossible)?
MfG
Goswin
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