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Subject: Re: [Qemu-devel] vhost-net issue with multiples interfaces using MQ
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To: William Dauchy <william@gandi.net>, QEMU Developers <qemu-devel@nongnu.org>

On 08/18/2014 07:42 PM, William Dauchy wrote:
> Hello,
>
> Using qemu2.1.0, a linux v3.14.X x86_64 as host and a linux v3.12.X x86_64 as guest
> I'm starting a VM with these network interfaces:
>
> [netdev "vifA.0"]
>   type = "tap"
>   vhost = "on"
>   ifname = "vifA.0"
>   downscript = "no"
>   script = "no"
>   queues = "2"
>
> [device "vifA.0"]
>   driver = "virtio-net-pci"
>   netdev = "vifA.0"
>   mac = "00:16:3e:1a:4e:11"
>   mq = "on"
>   vectors = "5"
>
> (and same config for two other interfaces but with a different MAC address)
>
> In the error message I'm getting during startup:
> unable to start vhost net: 95: falling back on userspace virtio

What's the qemu command line for your testing? I try simple command line
with 3 mq cards in qemu 2.1. Everything works fine.
> I saw that it's failing in `vhost_dev_start` where `vhost_dev_set_features` is returning an error.
> r = vhost_dev_set_features(hdev, hdev->log_enabled);
> I'm hitting the issue starting from three interfaces, i.e no problem with one or two.
> I also don't have the issue with disabling multi queue.
>
> Am I wrong on something? What can I do to help debug this situation?
>
> Regards,

Is this a regression? If yes, you can probably bisect to find the first
bad commit.

Thanks