https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254513
Bug ID: 254513
Summary: virtio_random: random_harvestq spinning on a CPU with
Q35 virtio random device
Product: Base System
Version: 13.0-STABLE
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: misc
Assignee: b...@freebsd.org
Reporter: m...@igalic.co
This virtual machine is running @ Hetzner on their CPX series, which uses the
Qemu Q35 chipset. Support for this has been recently added to FreeBSD and is in
FreeBSD 13.0.
The problem manifests as a load average of 1 on a 2 CPU system. `top -S` shows:
PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND
8 root 1 -16 - 0B 16K 0B CPU0 0 10:42 99.95%
rand_harvestq
So lets dig into the random device.
The device is identified like this:
grep -i entropy /var/run/dmesg.boot
vtrnd0: <VirtIO Entropy Adapter> on virtio_pci4
random: registering fast source VirtIO Entropy Adapter
meena@websrv2-hel1 ~> devinfo -p vtrnd0 -v
vtrnd0 pnpinfo vendor=0x00001af4 device=0x1044 subvendor=0x1af4
device_type=0x00000004
virtio_pci4 pnpinfo vendor=0x1af4 device=0x1044 subvendor=0x1af4
subdevice=0x1100 class=0x00ff00 at slot=0 function=0 dbsf=pci0:5:0:0
pci5
pcib5 pnpinfo vendor=0x1b36 device=0x000c subvendor=0x1b36 subdevice=0x0000
class=0x060400 at slot=2 function=4 dbsf=pci0:0:2:4
pci0
pcib0 pnpinfo _HID=PNP0A08 _UID=1 _CID=PNP0A03 at handle=\_SB_.PCI0
acpi0
nexus0
meena@websrv2-hel1 ~>
procstat kstack on rand_harvestq process looks like this:
8 100097 rand_harvestq - vtrnd_read random_kthread
fork_exit fork_trampoline
suggesting this is virtio_related
After adding
devmatch_blacklist="virtio_random.ko"
to rc.conf, and rebooting, the CPU spinning issue goes away.
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