Re: [Qemu-devel] vhost-net issue: does not survive reboot on ppc64

[Michael S. Tsirkin]

On Sun, Dec 22, 2013 at 02:01:23AM +1100, Alexey Kardashevskiy wrote:
> Hi!
> 
> I am having a problem with virtio-net + vhost on POWER7 machine - it does
> not survive reboot of the guest.
> 
> Steps to reproduce:
> 1. boot the guest
> 2. configure eth0 and do ping - everything works
> 3. reboot the guest (i.e. type "reboot")
> 4. when it is booted, eth0 can be configured but will not work at all.
> 
> The test is:
> ifconfig eth0 172.20.1.2 up
> ping 172.20.1.23
> 
> If to run tcpdump on the host's "tap-id3" interface, it shows no trafic
> coming from the guest. If to compare how it works before and after reboot,
> I can see the guest doing an ARP request for 172.20.1.23 and receives the
> response and it does the same after reboot but the answer does not come.

So you see the arp packet in guest but not in host?

One thing to try is to boot debug kernel - where pr_debug is
enabled - then you might see some errors in the kernel log.

> If to remove vhost=on, it is all good. If to try Fedora19
> (v3.10-something), it all good again - works before and after reboot.
> 
> 
> And there 2 questions:
> 
> 1. does anybody have any clue what might go wrong after reboot?
> 
> 2. Is there any good material to read about what exactly and how vhost
> accelerates?
> 
> My understanding is that packets from the guest to the real network are
> going as:
> 1. guest's virtio-pci-net does ioport(VIRTIO_PCI_QUEUE_NOTIFY)
> 2. QEMU's net/virtio-net.c calls qemu_net_queue_deliver()
> 3. QEMU's net/tap.c calls tap_write_packet() and this is how the host knows
> that there is a new packet.
> 
> 
> Thanks!
> 
> 
> This how I run QEMU:
> ./qemu-system-ppc64 \
> -enable-kvm \
> -m 2048 \
> -machine pseries \
> -initrd 1.cpio \
> -kernel vml312_virtio_net_dbg \
> -nographic \
> -vga none \
> -netdev
> tap,id=id3,ifname=tap-id3,script=ifup.sh,downscript=ifdown.sh,vhost=on \
> -device virtio-net-pci,id=id4,netdev=id3,mac=C0:41:49:4b:00:00
> 
> 
> That is bridge config:
> address@hidden ~]$ brctl show
> bridge name   bridge id               STP enabled     interfaces
> brtest                8000.00145e992e88       no      pin     eth4
> 
> 
> The ifup.sh script:
> ifconfig $1 hw ether ee:01:02:03:04:05
> /sbin/ifconfig $1 up
> /usr/sbin/brctl addif brtest $1
> 
> 
> 
> 
> -- 
> Alexey