Re: [Qemu-devel] Error: virtio_net: Too few free TX rings available.

[Bo YU]

Hello,
On Thu, Jun 14, 2018 at 11:47:44AM +0800, Bo YU wrote:
> Hello,
> A am newbie to qemu.
> I am using qemu now:
> qemu-io --version
> qemu-io version 2.12.50 (v2.12.0-1296-g2ab09bf2f9-dirty)
> Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers
>
> I have to talk about using qemu with libvirt recently libvirt deadlocked
> when libvirt fetching qemu capabilities.Under Michal Privoznik help, i
> restart my VM.
>
> The reason which cause recompile  qume from version 2.8 is:
> i want to modify some features:
>
> Fowllowing the instrustions:
>
> http://cilium.readthedocs.io/en/latest/bpf/#bpftool
>
> $ clang -O2 -Wall -target bpf -c xdp-example.c -o xdp-example.o
>
> I get the error:
>
> # sudo /sbin/ip link set dev ens3 xdp obj xdp_2.o
> Error: virtio_net: Too few free TX rings available.
> # sudo dmesg
> virtio_net virtio0 ens3: request 4 queues but max is 1
>
>
> And i type: sudo ethtool -g ens3
> Ring parameters for ens3:
> Pre-set maximums:
> RX: 256
> RX Mini:0
> RX Jumbo:0
> TX:256
> Current hardware settings:
> RX:256
> RX Mini:0
> RX Jumbo:0
> TX:256
>
> sudo ethtool -G ens3 rx 512
> Cannot set device ring parameters: Operation not supported
>
>
> I have trace the mail-list:
> https://bugzilla.redhat.com/show_bug.cgi?id=1301548
> and there:
> https://groups.google.com/forum/#!topic/snabb-devel/ng78LbcaFgII
> I remeber there is a patch for qemu for modfing paramertes in
> hw/virtio-net.c,sorry, i can't find the patch.
>
> If i modify the rx_queue_max by hand to 1024, Is it ok?
qemu-io  --version
qemu-io version 2.12.50 (v2.12.0-1296-g2ab09bf2f9-dirty)
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers

Under the above version of qemu,i modifyi and recompile qemu:
+#define VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE 1024
in hw/net/virtio-net.c
Now, i have got the result:

sudo ethtool -g ens3
[sudo] password for yubo-2:
Ring parameters for ens3:
Pre-set maximums:
RX:   1024
RX Mini:0
RX Jumbo:0
TX:   1024
Current hardware settings:
RX:    1024
RX Mini:0
RX Jumbo:0
TX:    1024

If you want to test xdp expertiment,maybe you have to do it follow below.

https://marc.info/?l=xdp-newbies&m=14948693111365&w=2

Here is the right incantation to add to the "interface" section(with 4 vcpus)
<driver name='vhost' queue='8'>
        <host tso4='off' tso6='off' ecn='off' ufo='off'/>
        <guest tso4='off' tso6='off' ecn='off' ufo='off'/>
</driiver>

Bo
> Thank you in advance!