[Xen-users] RE: [Xen-devel] Modular Xen

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

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]. 

--
Mats

> 
> regards,
> daniel
> 
> -- 
> Daniel Stodden
> LRR     -      Lehrstuhl für Rechnertechnik und Rechnerorganisation
> Institut für Informatik der TU München             D-85748 Garching
> http://www.lrr.in.tum.de/~stodden         mailto:stodden@xxxxxxxxxx
> PGP Fingerprint: F5A4 1575 4C56 E26A 0B33  3D80 457E 82AE B0D8 735B
> 



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