OK, bisect point me to this commit: # git bisect bad 7d37d351dffee60fc7048bbfd8573421f15eb724 is the first bad commit commit 7d37d351dffee60fc7048bbfd8573421f15eb724 Author: Jan Kiszka <jan.kis...@siemens.com> Date: Thu May 17 10:32:39 2012 -0300
virtio/vhost: Add support for KVM in-kernel MSI injection Make use of the new vector notifier to track changes of the MSI-X configuration of virtio PCI devices. On enabling events, we establish the required virtual IRQ to MSI-X message route and link the signaling eventfd file descriptor to this vIRQ line. That way, vhost-generated interrupts can be directly delivered to an in-kernel MSI-X consumer like the x86 APIC. Signed-off-by: Jan Kiszka <jan.kis...@siemens.com> Signed-off-by: Avi Kivity <a...@redhat.com> :040000 040000 1734ddc60cd8a85c7187e93e5a4c02e6d7706cf8 f417e63a684f3b92f5ff35d256962a2490890f00 M hw This obviously breaks vhost when using multiple cores. > -----Original Message----- > From: Peter Lieven [mailto:lieven-li...@dlhnet.de] > Sent: Dienstag, 06. November 2012 08:47 > To: Dietmar Maurer > Cc: Stefan Hajnoczi; qemu-devel@nongnu.org; Michael S. Tsirkin > Subject: Re: [Qemu-devel] slow virtio network with vhost=on and multiple > cores > > Dietmar Maurer wrote: > >> > ./x86_64-softmmu/qemu-system-x86_64 -smp sockets=1,cores=2 -m > 512 - > >> hda > >> > debian-squeeze-netinst.raw -netdev > >> > type=tap,id=net0,ifname=tap111i0,vhost=on -device > >> > virtio-net-pci,netdev=net0,id=net0 > >> > > >> > Downloading a larger file with wget inside the guest will show the > >> problem. > >> Speed drops from 100MB/s to 15MB/s. > >> > > >> > Can someone reproduce that bug? Any ideas how to fix that? > >> > >> Which exact QEMU are you using: qemu or qemu-kvm? Distro package or > >> from source? Any patches applied? > > > > I just tested with latest sources from > > git://git.qemu-project.org/qemu.git > > > > ./x86_64-softmmu/qemu-system-x86_64 -smp sockets=1,cores=2 -m 512 - > hda > > debian-squeeze-netinst.raw -netdev > > type=tap,id=net0,ifname=tap111i0,vhost=on -device > > virtio-net-pci,netdev=net0,id=net0 --enable-kvm > > > > got incredible bad performance - can't you reproduce the problem? > > I have seen a similar problem, ...