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

[Chao Gao]

On Mon, Aug 08, 2016 at 04:57:14PM +0800, Peter Xu wrote:
>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.

It doesn't work. My host machine has 16 cpus. When I assign 4 or 8 vcpus to the 
guest
or 255 vcpus but set "kernel-irqchip=off", the guest work well. Maybe when 
irqchip
is in kernel, intremap can only handle situations that vcpus number is less 
than 
physical cpus'. Do you think it's right? 

Thanks,
-Chao