[Qemu-discuss] virtio-scsi really slow init with ArchLinux kernel

[Chris]

I'm getting a 15 second delay on every VM boot when using the
ArchLinux kernel and using the virtio-scsi-pci system.

QEMU emulator version 2.12.0 running on Arch Linux (4.17.4 kernel),
booting the same.

I run qemu like so:

qemu-system-x86_64 \
   -nodefaults \
   -machine type=pc,accel=kvm -smp cores=2,threads=1 -cpu host -vga
vmware -m 2G \
   -device virtio-scsi-pci,id=scsi0,num_queues=2 \
   -drive 
id=hdroot,file=archlinux.qcow2,if=none,media=disk,cache=unsafe,format=qcow2
\
   -device scsi-hd,drive=hdroot

See the 15 second hang here:

[    0.577018] scsi host2: Virtio SCSI HBA
[    0.578413] scsi 2:0:0:0: Direct-Access     QEMU     QEMU HARDDISK
  2.5+ PQ: 0 ANSI: 5
[    1.333550] tsc: Refined TSC clocksource calibration: 2800.036 MHz
[    1.335351] clocksource: tsc: mask: 0xffffffffffffffff max_cycles:
0x285c62b0192, max_idle_ns: 440795270636 ns
[   17.134876] sd 2:0:0:0: Power-on or device reset occurred
[   17.137683] sd 2:0:0:0: [sda] 104857600 512-byte logical blocks:
(53.7 GB/50.0 GiB)
[   17.139845] sd 2:0:0:0: [sda] Write Protect is off
[   17.140791] sd 2:0:0:0: [sda] Mode Sense: 63 00 00 08
[   17.140921] sd 2:0:0:0: [sda] Write cache: enabled, read cache:
enabled, doesn't support DPO or FUA
[   17.143968]  sda: sda1 sda2

This is specific to the Arch Linux kernel and the virtio-scsi system.
IDE boots fast. If I boot an Ubuntu kernel with the exact same
virtio-scsi settings then there is no delay for the "Power-on or
device reset occurred" and it boots instantly.

Anyone know what is going on or what I can do to debug this?

Thanks