[dpdk-dev] KNI as kernel vHost backend failing

[sai kiran <kiransaiv@gmail.com>]

Hi,



We are trying to experiment with DPDK’s KNI application, with KNI working
as Kernel vHost backend.


1.  After starting the KNI application, KNI application has detected link
up.


*[root@localhost kni]# ./build/app/kni -c 0xf0 -n 4 -- -p 0x3 -P
--config="(0,4,6),(1,5,7)"*


APP: Initialising port 0 ...

KNI: pci: 10:00:01       8086:10fb

APP: Initialising port 1 ...

PMD: To improve 1G driver performance, consider setting the TX WTHRESH
value to 4, 8, or 16.

KNI: pci: 16:00:01       8086:10e7

Checking link status

.................................done

Port 0 Link Up - speed 10000 Mbps - full-duplex

Port 1 Link Up - speed 1000 Mbps - full-duplex

APP: Lcore 5 is reading from port 1

APP: Lcore 7 is writing to port 1

APP: Lcore 6 is writing to port 0

APP: Lcore 4 is reading from port 0


2. As mentioned in Programming guide, *sock_en* variable in sysfs is
enabled and a fd is generated

[root@localhost dpdk-1.7.1]# cat /sys/class/net/vEth0/sock_en
1
[root@localhost dpdk-1.7.1]# cat /sys/class/net/vEth1/sock_en
1
[root@localhost dpdk-1.7.1]# cat /sys/class/net/vEth0/sock_fd
11
[root@localhost dpdk-1.7.1]# cat /sys/class/net/vEth1/sock_fd
12

3. But when a VM is launched with this file-descriptor as the
vhost-backend, the qemu-kvm is throwing an ioctl-failure error. This ioctl
is making the vhost-backend fallback to virtio-userspace.



[root@localhost qemu-kvm-1.2.0]# /usr/bin/qemu-kvm -m 2048 -enable-kvm -cpu
host -smp 2 -name VSK1 -drive file=/root/SAI/NSVPX-KVM-11.0-28.1_nc.raw
-netdev tap,fd=12,id=mynet_kni,vhost=on -device
virtio-net-pci,netdev=mynet_kni,bus=pci.0,addr=0x4,ioeventfd=on

qemu-kvm: -netdev tap,fd=12,id=mynet_kni,vhost=on: TUNGETIFF ioctl()
failed: Bad file descriptor

TUNSETOFFLOAD ioctl() failed: Bad file descriptor

qemu-kvm: unable to start vhost net: 88: falling back on userspace virtio

qemu-kvm: unable to start vhost net: 88: falling back on userspace virtio

qemu-kvm: unable to start vhost net: 88: falling back on userspace virtio

With this failure, the traffic from VM is not flowing through KNI interface.



The above mentioned ioctl failure does NOT happen consistently. During the
instances when failure is not seen, traffic flows successfully through the
KNI interfaces.



Can someone please shed some light as to what is happening in this case.
Are we missing something here? Is there a known issue?



Thanks,

Kiran



-- 
*Saikiran V*