[Qemu-devel] Problem with high load average when using -nographic with qemu in background

[Phil Rasch <phil@supstitches.com>]

Sorry to bother you with this. I did try the qemu forums first.

I am having trouble running a trixbox/centos guest under an ubuntu host. Both 
completely uptodate installs of the OS's. I am using Qemu 0.8.2 with 
kqemu-1.3.0pre9.

If I start the qemu without -nographic interactively the VM runs well, and the 
hostOS maintains a load average of about 0.1

Trouble comes when I add -nographic to the command line, and redirect stdout 
and stderrout to a logfile. (I do this so I can start qemu from during the 
boot up process and run the VM in background all the time.

If I start qemu like this (from an interactive shell (tcsh))
qemu -m 256 -localtime -net nic -net tap -nographic trixbox.img \ 
>&! /tmp/qemulog &

It will stop on
 + Suspended[tty output]

If I also redirect stdin (eg adding "< /dev/null") it then starts and runs 
fine, but the hostOS load climbs to 1.0 and higher (depending on what the 
guest is doing, and the performance of the VM is seriously impaired.

I can ssh into the machine under both scenarios and see that the guest thinks 
it is fine, but it is really burdening the hostOS.

Looking through /var/log/messages on the guest shows that I have (I think) 
successfully set io to go through /dev/ttyS0, eg.

Jan  6 09:46:49 asterisk1 kernel: Kernel command line: ro console=ttyS0,9600n8 
vga=normal root=LABEL=/

Can anyone offer advice?

Phil