NetBSD/i386 6.0 guest suffers interrupt storm since qemu BIOS update

[Andreas Gustafsson]

Since the pc-bios update of qemu commit d7a51dbbaa70677846453f8c961590913052dd86, booting a NetBSD/i386 guest takes a very long time, apparently due to interrupt load.

For example, booting the NetBSD/i386 6.0 serial console install CD with

  wget ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-6.0/i386/installation/cdrom/boot-com.iso
  qemu-system-i386 -nographic -cdrom boot-com.iso

used to take less than a minute, but now takes more like ten minutes to enter the "sysinst" installer; it's so slow that at first I thought it had hung. If I then exit the installer and type "vmstat -i", it shows a high interrupt rate on ioapic0 pin 9:

# vmstat -i
interrupt total rate
cpu0 timer 336942 102
ioapic0 pin 9 256791232 78052
ioapic0 pin 1 1 0
ioapic0 pin 15 345 0
ioapic0 pin 4 102 0
ioapic0 pin 6 1 0
Total 257128623 78154

According to dmesg, this is the piixpm0 device:

# dmesg
[...]
piixpm0 at pci0 dev 1 function 3: vendor 0x8086 product 0x7113 (rev. 0x03)
timecounter: Timecounter "piixpm0" frequency 3579545 Hz quality 1000
piixpm0: 24-bit timer
piixpm0: interrupting at ioapic0 pin 9
[...]

Versions of qemu lacking commit d7a51dbbaa70677846453f8c961590913052dd86 do not have this problem.

[Andreas Gustafsson (gson)]

The bug has been fixed; revisoion 5928023cef87847a295035487397b9ec701fdd6b is still broken, but dbd99ae302be8f51b547fb6283c91d0c9859b7d5 works. I haven't determined which of the commits inbetween fixed it, but the BIOS update of 15faf946f7a17a5fab0d05a2312d43249d81af3 seems like a likely candidate.