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Re: [Qemu-devel] tap devices not receiving packets from a bridge

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] tap devices not receiving packets from a bridge
Date: Thu, 16 May 2013 09:24:05 +0300

On Wed, May 15, 2013 at 12:00:03PM +0100, Nicholas Thomas wrote:
> Hi again,
> On Tue, 2013-05-14 at 15:49 +0100, Nicholas Thomas wrote:
> > /sys/devices/virtual/net/t100/tun_flags is 0x5002 - so it looks like
> > IFF_ONE_QUEUE was indeed unset by qemu (which is lacking the patch). It
> > surprises me, but that's probably my fault, rather than qemu's.
> I've rebuilt 1.4.1 with the IFF_ONE_QUEUE patch and tun_flags is now
> 0x7002; unfortunately, I'm still seeing this bug, twice in five trials.
> Symptoms in `ifconfig t100` now differ; overruns stays at 0, and
> "dropped" increases monotonically as I send packets. Those packets do
> appear if I tcpdump t100 on the host, but not if I tcpdump t100 on the
> guest.
> I've turned off gro in the guest, which makes no difference, and tried
> changing the queue sizes (post-hoc) in both guest and host, in the hope
> of causing them to be emptied out, clearing the condition; again to no
> effect.
> The VMs in question are bridged to a large (and busy) VLAN with no
> ingress filtering to speak of; I guess what's happening is that the
> transmit queue is filled up by that traffic while the guest is in ipxe,
> and it never gets out of that state when it happens... so maybe there is
> still an underlying problem?
> /Nick

Is this with or without vhost-net in host?


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