From: Dan Magenheimer <dan.magenheimer@oracle.com>
To: "\"Pasi Kärkkäinen\"" <pasik@iki.fi>,
"Jan Beulich" <JBeulich@novell.com>
Cc: xen-devel@lists.xensource.com,
Martin Lukasik <martin.lukasik@cancer.org.uk>
Subject: RE: Xen CPU limit?
Date: Tue, 30 Mar 2010 09:14:54 -0700 (PDT) [thread overview]
Message-ID: <43f035b5-977e-4910-a46e-608d76a9346f@default> (raw)
In-Reply-To: <20100330075306.GY1878@reaktio.net>
> -----Original Message-----
> From: Pasi Kärkkäinen [mailto:pasik@iki.fi]
> Sent: Tuesday, March 30, 2010 1:53 AM
> To: Jan Beulich
> Cc: xen-devel@lists.xensource.com; Martin Lukasik
> Subject: Re: [Xen-devel] Xen CPU limit?
>
> On Tue, Mar 30, 2010 at 08:16:26AM +0100, Jan Beulich wrote:
> > >>> Pasi Kärkkäinen<pasik@iki.fi> 29.03.10 17:49 >>>
> > >I think the number of virtual cpus (vcpus) per guest is (was) 32,
> > >and now in Xen 4.0.0 you can have up to 64 vcpus per guest.
> >
> > I don't think the tools are up to anything beyond 32 yet.
>
> Hmm.. what's actually missing from the tools to handle >32 vcpus?
>
> > The (64-bit) hypervisor allows up to 8192 vCPU-s iirc (but that's a
> truly
> > theoretical limit, as Dom0 or a guest likely won't be able to bring
> up
> > that many due to there only being 4096 event channels; current
> > Linux requires 5-6 of them per vCPU for IPIs and timer vIRQ).
> >
>
> Wow.. I wasn't aware the (theoretical) limit is that big :)
But, if I am reading this correctly, 4096 event channels
is the next scalability barrier. If, on a "big" machine, one
tries to run 64 (nearly always idle) guests each configured
with 16 vcpus (because they run a busy database load when
they are not idle), it won't work due to the event channel limit?
This scenario seems quite possible in a cloud/hosting environment.
next prev parent reply other threads:[~2010-03-30 16:14 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-11 16:08 Xen CPU limit? Martin Lukasik
2010-03-29 15:49 ` Pasi Kärkkäinen
2010-03-30 7:16 ` Jan Beulich
2010-03-30 7:53 ` Pasi Kärkkäinen
2010-03-30 8:56 ` Jan Beulich
2010-03-30 16:14 ` Dan Magenheimer [this message]
2010-03-31 7:11 ` Jan Beulich
2010-03-30 9:16 ` Martin Lukasik
2010-03-30 9:23 ` Keir Fraser
2010-03-30 9:26 ` Pasi Kärkkäinen
2010-03-30 9:32 ` Martin Lukasik
2010-03-30 9:39 ` Pasi Kärkkäinen
2010-03-30 9:43 ` Keir Fraser
2010-03-29 16:00 ` Jan Beulich
2010-03-29 16:03 ` Martin Lukasik
2010-03-29 16:17 ` Jan Beulich
2010-03-29 16:27 ` Keir Fraser
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