On Tue, Aug 09, 2016 at 02:18:15PM +0800, Peter Xu wrote: > On Tue, Aug 09, 2016 at 12:33:17PM +0800, Chao Gao wrote: > > 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? > > I don't think so. Vcpu number should not be related to host cpu > numbers. > > I think the problem is with x2apic. Currently, x2apic is enabled in > vIOMMU when kernel irqchip is used. This is problematic, since > actually we are throughing away dest_id[31:8] without Radim's patches, > meanwhile I see that by default x2apic is using cluster mode. > > In cluster mode, 8 bits will possibly not suffice (I think the reason > why >17 vcpus will bring trouble is that each cluster has 16 vcpus, > we'll have trouble if we have more than one cluster). > > To temporarily solve your issue, you should not only need "-global > ioapic.version=0x20" in QEMU command line, but also add "x2apic_phys" > to you guest kernel boot parameter, to force guest boot with x2apic > physical mode (not cluster mode). Though this can only work for <255 > vcpus. IMHO we may still need to wait for Radim's patches to test >255 > case.
Not sure whether we should temporarily disable EIM by default for now (provide an extra flag to optionally enable it)? Since it might break guests with >17 vcpus. CC Jan as well. -- peterx
