Re: [Qemu-devel] [PATCH for-2.8 00/18] pc: q35: x2APIC support in kvm_apic mode

[Peter Xu]

On Mon, Aug 08, 2016 at 03:41:23PM +0800, Chao Gao wrote:
> HI, everyone.
> 
> We have done some tests after merging this patch set into the lastest qemu
> master. In kvm aspect, we use the lastest kvm linux-next branch. Here are
> some problems we have met.
> 
> 1. We can't boot up a 288 vcpus linux guest with CLI:
> qemu-system-x86_64 -boot c -m 4096 -sdl -monitor pty --enable-kvm \
> -M kernel-irqchip=split -serial stdio -bios bios.bin -smp cpus=288 \
> -hda vdisk.img -device intel-iommu,intremap=on -machine q35.
> The problem exists, even after we only assign 32 vcpus to the linux guest.
> Maybe the output "do_IRQ: 146.113 No irq handler for vector (irq -1)" is a 
> clue.
> The output of qemu and kernel is in attachments. Do you have any idea
> about the problem and how to solve it?

IIUC, we need to wait for Radim's QEMU patches to finally enable 288
vcpus?

Btw, could you please try adding this to the QEMU cmdline when testing
with 32 vcpus:

  -global ioapic.version=0x20

I see that you were running RHEL 7.2 guest with a default e1000. In
that case, we may need to boost ioapic version to 0x20.

Thanks,

-- peterx