[Qemu-devel] QEMU -netdev vhost=on + -device virtio-net-pci bug

[Alexey Kardashevskiy <aik@ozlabs.ru>]

Hi!

The patch f56a12475ff1b8aa61210d08522c3c8aaf0e2648 "vhost: backend masking 
support" breaks virtio-net + vhost=on on PPC64 platform.

The problem command line is:
1) -netdev tap,id=tapnet,ifname=tap0,script=qemu-ifup.sh,vhost=on \
-device virtio-net-pci,netdev=tapnet,addr=0.0 \

Without the patch, the eth0 in the guest works fine, with the patch it 
simply does not. The guest's eth0 also works with the following configs:

2) new -netdev interface with vhost=off:
-netdev tap,id=tapnet,ifname=tap0,script=qemu-ifup.sh \
-device virtio-net-pci,netdev=tapnet,addr=0.0

3) old -net interface with vhost=on:
-net tap,ifname=tap0,script=qemu-ifup.sh,vhost=on \
-net nic,model=virtio,addr=0:0:0

4) old -net interface with vhost=off:
-net tap,ifname=tap0,script=qemu-ifup.sh \
-net nic,model=virtio,addr=0:0:0

I run http://junkcode.samba.org/ftp/unpacked/junkcode/socklib/ on
10Gb ethernet and observe 1020MB/s for 1) (without the patch),
800MB/s for 2), 70MB/s for 3) and 4).

The virtio features (cat /sys/bus/virtio/devices/virtio0/features)
for 1) and 2) are:
"1100011111111111111100000000110000000000000000000000000000000000"
and for 3) and 4) they are:
"0000011000000001111100000000110000000000000000000000000000000000"


I guess this is because the old -net interface creates
an internal hub as "info qtree" shows vlan=0 and netdev=hub0port1
while the new -netdev interface does not seem to create any internal
hub (vlan=<null>, netdev=tapnet). btw why are the configs so different?

The network config is below. Both host and guest are running 3.8 kernel.
The qemu tree from qemu.org/master still has this problem.


What am I missing? Thanks.


The full command line is like below plus the network config from
the examples above:

sudo qemu-impreza/ppc64-softmmu/qemu-system-ppc64 -m 1024 -machine 
pseries,kernel_irqchip=on -trace events=trace_events \
-nographic -vga none -enable-kvm -kernel vml38_64k -initrd 1.cpio


This is the host config:

[aik@vpl2 ~]$ cat qemu-ifup.sh
#! /bin/sh

/sbin/ifconfig $1 0.0.0.0 promisc up
/usr/sbin/brctl addif brtest $1

[aik@vpl2 ~]$ brctl show
bridge name	bridge id		STP enabled	interfaces
brtest		8000.00145e992e88	no		eth0
[aik@vpl2 ~]$ ifconfig eth0
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
         inet6 fe80::214:5eff:fe99:2e88  prefixlen 64  scopeid 0x20<link>
         ether 00:14:5e:99:2e:88  txqueuelen 1000  (Ethernet)
         RX packets 1781219  bytes 124692636 (118.9 MiB)
         RX errors 0  dropped 0  overruns 0  frame 0
         TX packets 13734906  bytes 20755102658 (19.3 GiB)
         TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
         device interrupt 49  memory 0x3c0500800000-3c0500800fff

[aik@vpl2 ~]$ lspci -vs 1:1:0.0
0001:01:00.0 Ethernet controller: Chelsio Communications Inc T310 10GbE 
Single Port Adapter
	Subsystem: IBM Device 038c
	Flags: bus master, fast devsel, latency 0, IRQ 49
	Memory at 3c0500800000 (64-bit, non-prefetchable) [size=4K]
	Memory at 3c0500000000 (64-bit, non-prefetchable) [size=8M]
	Memory at 3c0500801000 (64-bit, non-prefetchable) [size=4K]
	[virtual] Expansion ROM at 3c0500c00000 [disabled] [size=512K]
	Capabilities: <access denied>
	Kernel driver in use: cxgb3

[aik@vpl2 ~]$ ls -l /sys/bus/pci/devices/0001\:01\:00.0/net/
total 0
drwxr-xr-x. 5 root root 0 Mar  5 12:59 eth0
[aik@vpl2 ~]$ uname -a
Linux vpl2.ozlabs.ibm.com 3.8.0-kvm-64k-aik+ #239 SMP Tue Mar 5 12:50:05 
EST 2013 ppc64 ppc64 ppc64 GNU/Linux


This is the running guest:

root@erif_root:~# lspci -v
00:00.0 Ethernet controller: Qumranet, Inc. Virtio network device
	Subsystem: Qumranet, Inc. Device 0001
	Flags: bus master, fast devsel, latency 0, IRQ 19
	I/O ports at 0020 [size=32]
	Memory at 100b0000000 (32-bit, non-prefetchable) [size=4K]
	Expansion ROM at 100b0010000 [disabled] [size=64K]
	Capabilities: [40] MSI-X: Enable+ Count=3 Masked-
	Kernel driver in use: virtio-pci

root@erif_root:~# ifconfig -a
eth0      Link encap:Ethernet  HWaddr 52:54:00:12:34:56
           inet addr:172.20.1.2  Bcast:172.20.255.255  Mask:255.255.0.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:36 errors:0 dropped:6 overruns:0 frame:0
           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:2268 (2.2 KiB)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback
           inet addr:127.0.0.1  Mask:255.0.0.0
           UP LOOPBACK RUNNING  MTU:65536  Metric:1
           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

root@erif_root:~# uname -a
Linux erif_root 3.8.0-aik-guest+ #262 SMP Mon Mar 4 15:58:55 EST 2013 ppc64 
GNU/Linux


-- 
Alexey