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

[Mark McLoughlin <markmc@redhat.com>]

On Tue, 2008-09-09 at 13:11 +0200, Henrik Holst wrote:
> tis 2008-09-09 klockan 11:47 +0100 skrev Mark McLoughlin:
> > 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.
> 
> So is it the host kernel that should be patched?

Yes.

(Or build qemu-kvm to not use signalfd)

Cheers,
Mark.