From: Avi Kivity <avi@redhat.com>
To: John Paul Walters <jwalters@isi.edu>
Cc: kvm@vger.kernel.org
Subject: Re: KVM cpu limitations
Date: Tue, 09 Aug 2011 12:13:26 +0300 [thread overview]
Message-ID: <4E40FA36.5010006@redhat.com> (raw)
In-Reply-To: <177F19C3-BF92-4641-B3BC-F7CE1BFC38A0@isi.edu>
On 08/08/2011 10:18 PM, John Paul Walters wrote:
> On Jul 21, 2011, at 2:10 AM, Avi Kivity wrote:
>
> > On 07/21/2011 02:20 AM, John Paul Walters wrote:
> >> Hi,
> >>
> >> We have a 256 core SGI Ultraviolet machine running RHEL 6.1 with qemu-kvm 0.13, and we'd like to be able to start large guest VMs of up to 256 cores. I see that x86 guests are currently limited to 64 VCPUs. Is there any reason for this hard limitation? It appears that we can't get around this limitation by simply redefining the kernel's KVM_MAX_VCPUS to 256. Qemu-kvm and possibly SeaBIOS seem to require changes as well. Can anyone offer any suggestions as to how straightforward it would be to increase the number of CPUs that we can allocate to KVM guests?
> >>
> >
> > And here I am on record saying no one wants this...
> >
> > kvm.git has patches increasing the limit to 254 (256 is not possible due to the APIC ID being 8 bits and two IDs being reserved).
> >
> > Latest seabios appears to have no cpu limits; qemu is limited to 255.
> >
>
>
> Hi again,
>
> I've applied the 254 core patches (below) from kvm.git on a RHEL 6.1 kernel. The new modules build and insert fine.
>
> https://git.kernel.org/?p=virt/kvm/kvm.git;a=commit;h=052fa7f4c5e79262cffcdc90bdd94172e00d45e3
> https://git.kernel.org/?p=virt/kvm/kvm.git;a=commit;h=29a07f8e31980599c586ea7d1f84957bc7fe98ed
>
> However, whenever I try to boot a system with more than 83 CPUs, the system fails to boot with:
>
> Booting from Hard Disk...
> Boot failed: could not read the boot disk
>
> I'm using qemu-kvm.git with the following command line:
> /opt/qemu.git/bin/qemu-system-x86_64 -smp 84 -hda big_image_2.qcow2 -m 8388 -redir tcp:52109::22
>
> Does anyone have any suggestions?
>
>
Most likely a seabios failure. Suggest you enable debugging in seabios
and see what's going on; also copy the seabios mailing list.
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2011-08-09 9:13 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-20 23:20 KVM cpu limitations John Paul Walters
2011-07-21 6:10 ` Avi Kivity
2011-08-08 19:18 ` John Paul Walters
2011-08-09 9:13 ` Avi Kivity [this message]
2011-08-09 18:32 ` John Paul Walters
2011-08-10 3:04 ` Kevin O'Connor
2011-08-10 20:43 ` John Paul Walters
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4E40FA36.5010006@redhat.com \
--to=avi@redhat.com \
--cc=jwalters@isi.edu \
--cc=kvm@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox