[libvirt-users] busy loop in libvirtd (cpu usage 100%)

[Igor Serebryany]

Hi!

	Occasionally of late, I've seen a few cases where libvirtd cpu usage
	shoots up to 100% and stays there indefinitely. This seems to happen
	when a QEMU VM is starting up, although on one occasion I *think* I
	saw it happen after a QEMU VM was p2p-migrated. 

	Doing strace -f -p <libvirtd pid> reveals a flood of poll() functions calls
	like these: 

[pid  1690] poll([{fd=3, events=POLLIN}, {fd=6, events=POLLIN}, {fd=12, events=POLLIN|POLLERR|POLLHUP}, {fd=11, events=POLLIN|POLLERR|POLLHUP}, {fd=10, events=POLLIN|POLLERR|POLLHUP}, {fd=9, events=POLLIN|POLLERR|POLLHUP}, {fd=24, events=POLLIN|POLLERR|POLLHUP}, {fd=21, events=POLLOUT}, {fd=14, events=POLLIN}, {fd=15, events=POLLIN}, {fd=16, events=POLLIN}, {fd=17, events=POLLIN}, {fd=21, events=POLLIN|POLLERR|POLLHUP}, {fd=20, events=POLLIN|POLLERR|POLLHUP}], 14, -1) = 1 ([{fd=21, revents=POLLOUT}])

	It seems that because 1 is returned each time, libvirtd just goes
	crazy dealing with fd-3, but I have no idea what fd-3 is.

	Restarting libvirtd fixes the high load, and then everything just
	goes back to chugging along as usual.

	This is on libvirt 0.8.5 with qemu 0.12.5 on a debian Squeeze system
	(the libvirt is compiled by hand).

	I'm not sure what's causing it, whether it's a bug in my own code
	somehow or inside libvirtd. I'd appreciate some help on how to debug
	this problem further -- restarting libvirtd is kind of a pain for
	me, because my application, which monitors the health on the node,
	maintains open connections to 'qemu:///system' and would thus have
	to restart itself as well...

--Igor
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