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? thanks, JP > -- > I have a truly marvellous patch that fixes the bug which this > signature is too narrow to contain. > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
