Re: massive performance drop after a while when using virtio nics

[Mark McLoughlin <markmc@redhat.com>]

On Tue, 2008-09-09 at 12:32 +0200, Fabian Deutsch wrote:
> Am Dienstag, den 09.09.2008, 11:22 +0100 schrieb Mark McLoughlin:
> > Hi,
> > 
> > On Sat, 2008-08-23 at 21:21 +0200, Fabian Deutsch wrote:
> > > Hey.
> > > 
> > > When running a guest in the following setup, I observ a "massive"
> > > performance decrease after a couple of gigabytes of transfrerred data.
> > > 
> > > other guests keep running fine (no regressions) and nothing unusual is
> > > observed on the host.
> > 
> > If you do "killall -ALRM qemu-kvm" after the slowdown has occurred, does
> > it make things speed up again for a while?
> > 
> 
> It seems so! 
> Fantastic.
> 
> > If so, the issue is fixed by:
> > 
> >   http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=ba661292a2bc6ddd305a212b0526e5dc22195fe7
> > 
> > It also got applied in 2.6.26.3 and 2.6.25.16.
> > 
> 
> So it was some signaling-bug on the .. client side?

No, it was a kernel race condition causing the qemu-kvm process to stop
receiving SIGALRM signals.

The original thread might explain it a bit better:

  http://thread.gmane.org/gmane.comp.emulators.kvm.devel/19582

Cheers,
Mark.