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.
ok, after adding "x2apic_phys" to guest kernel boot parameter, I boot up a 288(yes, 288) vcpus guest successfully with command qemu-system-x86_64 -boot c -m 4096 -sdl --enable-kvm \ -M kernel-irqchip=split -bios bios.bin -smp cpus=288 -hda vdisk.img \ -device intel-iommu,intremap=on -machine q35 Also, I can see interrupts on those cpu with inital apicid>255 from /proc/cpuinfo and /proc/interrupts. Thanks. -Chao
