[Qemu-discuss] Qemu machine pc-q35-2.6 does not boot with 14 disks

[Vasudev Kamath]

Hi,

I've Qemu machine instance with 14 virtio-blk disks and 40 CPU's and
machine type
pc-q35-2.6. I've 2 cases of hypervisor OS, Debian 8 and Debian 9 and following
observations.

1. Host = Debian 8 Machine=pc-q35-2.6 Disks=14 Result=Boots
2. Host = Debian 9 Machine=pc-q35-2.6 Disks=14 Result=Hangs in boot
3. Host = Debian 9 Machine=pc-q35-2.7 or higher Disks=14 Result=Boots
4. Host = Debian 9 Machine=pc-q35-2.6 Disks=11 Result=Boots

We want the scenario 2 to work in our infrastructure but only reducing
the number of disks
as seen in scenario 4 is the only way to get system to boot.

In scenario 2 we observed qemu is showing ~4000% CPU usage. A couple of strace
from the various qemu threads is attached with this mail(kvm_run.txt).
I'm also attaching
domain xml generated by libvirt with this mail.

Below is the ps output of qemu process.

libvirt+ 6199 1 99 09:35 ? 1-01:14:02 qemu-system-x86_64 -enable-kvm
-name guest=vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99,debug-threads=on
-S -object 
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-48-vm-f6d5e119-cecb-4f2/master-key.aes
-machine pc-q35-2.6,accel=kvm,usb=off,dump-guest-core=off -cpu
Haswell-noTSX,+xsaveopt,+tsc_adjust,+vme,+dtes64,+vmx,+xtpr,+est,+monitor,+smx,+abm,+osxsave,+tm,+acpi,+arat,+ht,+dca,+pdcm,+pdpe1gb,+f16c,+ds,+invtsc,+tm2,+ss,+pbe,+ds_cpl,+rdrand
-m 98304 -realtime mlock=off -smp 40,sockets=2,cores=10,threads=2
-uuid 6872f338-fc7d-4322-9a33-3c9b16436f87 -no-user-config -nodefaults
-chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-48-vm-f6d5e119-cecb-4f2/monitor.sock,server,nowait
-mon chardev=charmonitor,id=monitor,mode=control -rtc
base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=delay -no-hpet
-no-shutdown -boot strict=on -device
ioh3420,port=0x10,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,addr=0x2
-device ioh3420,port=0x11,chassis=2,id=pci.2,bus=pcie.0,addr=0x2.0x1
-device ioh3420,port=0x12,chassis=3,id=pci.3,bus=pcie.0,addr=0x2.0x2
-device ioh3420,port=0x13,chassis=4,id=pci.4,bus=pcie.0,addr=0x2.0x3
-device ioh3420,port=0x14,chassis=5,id=pci.5,bus=pcie.0,addr=0x2.0x4
-device ioh3420,port=0x15,chassis=6,id=pci.6,bus=pcie.0,addr=0x2.0x5
-device ioh3420,port=0x16,chassis=7,id=pci.7,bus=pcie.0,addr=0x2.0x6
-device ioh3420,port=0x17,chassis=8,id=pci.8,bus=pcie.0,addr=0x2.0x7
-device 
ioh3420,port=0x18,chassis=9,id=pci.9,bus=pcie.0,multifunction=on,addr=0x3
-device ioh3420,port=0x19,chassis=10,id=pci.10,bus=pcie.0,addr=0x3.0x1
-device ioh3420,port=0x1a,chassis=11,id=pci.11,bus=pcie.0,addr=0x3.0x2
-device ioh3420,port=0x1b,chassis=12,id=pci.12,bus=pcie.0,addr=0x3.0x3
-device ioh3420,port=0x1c,chassis=13,id=pci.13,bus=pcie.0,addr=0x3.0x4
-device ioh3420,port=0x1d,chassis=14,id=pci.14,bus=pcie.0,addr=0x3.0x5
-device ioh3420,port=0x1e,chassis=15,id=pci.15,bus=pcie.0,addr=0x3.0x6
-device ioh3420,port=0x1f,chassis=16,id=pci.16,bus=pcie.0,addr=0x3.0x7
-device ioh3420,port=0x20,chassis=17,id=pci.17,bus=pcie.0,addr=0x4
-device ich9-usb-ehci1,id=usb,bus=pcie.0,addr=0x1d.0x7 -device
ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pcie.0,multifunction=on,addr=0x1d
-device ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pcie.0,addr=0x1d.0x1
-device ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pcie.0,addr=0x1d.0x2
-drive 
file=/dev/vgroot_ssd_m1/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-ssd-shared-m1-disk0,format=raw,if=none,id=drive-virtio-disk0,cache=none,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.2,addr=0x0,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
-drive 
file=/dev/vgroot_ssd_m1/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-ssd-shared-m1-disk1,format=raw,if=none,id=drive-virtio-disk1,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.3,addr=0x0,drive=drive-virtio-disk1,id=virtio-disk1
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk2,format=raw,if=none,id=drive-virtio-disk2,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.4,addr=0x0,drive=drive-virtio-disk2,id=virtio-disk2
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk3,format=raw,if=none,id=drive-virtio-disk3,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.5,addr=0x0,drive=drive-virtio-disk3,id=virtio-disk3
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk4,format=raw,if=none,id=drive-virtio-disk4,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.6,addr=0x0,drive=drive-virtio-disk4,id=virtio-disk4
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk5,format=raw,if=none,id=drive-virtio-disk5,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.7,addr=0x0,drive=drive-virtio-disk5,id=virtio-disk5
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk6,format=raw,if=none,id=drive-virtio-disk6,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.8,addr=0x0,drive=drive-virtio-disk6,id=virtio-disk6
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk7,format=raw,if=none,id=drive-virtio-disk7,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.9,addr=0x0,drive=drive-virtio-disk7,id=virtio-disk7
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk8,format=raw,if=none,id=drive-virtio-disk8,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.10,addr=0x0,drive=drive-virtio-disk8,id=virtio-disk8
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk9,format=raw,if=none,id=drive-virtio-disk9,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.11,addr=0x0,drive=drive-virtio-disk9,id=virtio-disk9
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk10,format=raw,if=none,id=drive-virtio-disk10,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.12,addr=0x0,drive=drive-virtio-disk10,id=virtio-disk10
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk11,format=raw,if=none,id=drive-virtio-disk11,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.13,addr=0x0,drive=drive-virtio-disk11,id=virtio-disk11
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk12,format=raw,if=none,id=drive-virtio-disk12,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.14,addr=0x0,drive=drive-virtio-disk12,id=virtio-disk12
-drive 
file=/home/sata/vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99-sata-dedicated-disk13,format=raw,if=none,id=drive-virtio-disk13,cache=none,discard=unmap,aio=native
-device 
virtio-blk-pci,scsi=off,bus=pci.15,addr=0x0,drive=drive-virtio-disk13,id=virtio-disk13
-netdev tap,fd=26,id=hostnet0,vhost=on,vhostfd=28 -device
virtio-net-pci,netdev=hostnet0,id=net0,mac=02:01:0a:21:b3:7a,bus=pci.1,addr=0x0
-chardev pty,id=charserial0 -device
isa-serial,chardev=charserial0,id=serial0 -vnc 0.0.0.0:0 -device
cirrus-vga,id=video0,bus=pcie.0,addr=0x1 -device
virtio-balloon-pci,id=balloon0,bus=pci.16,addr=0x0 -msg timestamp=on

Any help/pointers are greatly appreciated.

Thanks in Advance
-- 

Vasudev Kamath
https://copyninja.info

kvm_run.txt
Description: Text document

vm-f6d5e119-cecb-4f24-70b9-6d6c67430b99.xml
Description: Text Data