Re: [Xen-ia64-devel] [PATCH] Use saner dom0 memory and vcpu defaults, don't panic on over-allocation

[Alex Williamson <alex.williamson@xxxxxx>]

On Mon, 2007-08-06 at 10:11 -0400, Jarod Wilson wrote:
> Alex Williamson wrote: 
> >    I think we're going to have to go with something like this, but why
> > would we reduce the cap to 64MB?  I usually think of ia64 systems as
> > having "bigger" I/O than x86, so it seems like maybe we want to stick
> > with at least 128MB(?)
> 
> I think my original thought was that since your 96G box only needed
> really 17MB, 64MB was a ton to withhold. But after hitting send, I was
> thinking that no cap at all might make more sense -- you'd need 288GB of
> RAM to even get to 64MB here, and that's a tiny drop in the bucket when
> you have that much. Even with 1TB of RAM, we would still withhold less
> than 256MB. Until we have some 1TB+ systems to test on, we don't really
> know if reserving more than 128MB makes sense or not... I'd have to lean
> toward simply not capping this withholding at all, at least for right now.

   That sounds ok with me, we can continue to fine tune it via bug
reports if it's insufficient.

[snip]
> But then I don't know what the typical end-user use case of ia64 xen is,
> or what the average system size is, which would seem to be a fairly
> relevant factor in deciding the most reasonable defaults... My intuition
> says that most of our customers would like to have their systems boot up
> using all available resources though. That, and I'm already starting to
> feel like a 4G/4cpu default is a bit wimpy. :)

  It's ok to assign all memory and cpu to dom0 if you intend to use dom0
as a compute server, but that's not really the way dom0 is meant to be
used in a virtualized environment.  IIRC, dom0 has some scheduling
preference over domUs, and can therefore starve or reduce the
performance of the virtualized guests.  It's recommended that dom0 is
primarily used as a management domain for the other guests and not used
as your primary workload server.  IMHO, reducing the default set of
resources available to dom0 encourages this behavior.  Thanks,

        Alex

-- 
Alex Williamson                             HP Open Source & Linux Org.


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