OpenStack network tap interface random rxdrops for some VMs

hai wu haiwu.us at gmail.com
Mon Jul 19 17:54:37 UTC 2021


I already ensured txqueuelen for that VM's tap interface, and enabled
multi-queue for the VM, but its tap rxdrop still randomly kept
increasing, dropping one packet every few 10 or 20  or 60 seconds (It
makes sense to me, since that would only help with txdrops, not
rxdrops per my understandingj). This is an idle VM. After migrating
this idle VM to another idle OpenStack hypervisor, so it is only one
VM running on one dedicated physical OpenStack hypervisor, and now it
is dropping 0.03 rxdrops/s every 10 minutes.

I am not aware of any way to configure rxqueuelen for tap interface. I
assume tap RX -> Hypervisor RX -> VM TX, correct? How to tune
rxqueuelen for tap interface? If logging into this idle Linux test VM,
I am not seeing any drops, either in its RX or TX.

On Mon, Jul 19, 2021 at 12:03 PM Sean Mooney <smooney at redhat.com> wrote:
>
> On Mon, 2021-07-19 at 11:39 -0500, hai wu wrote:
> > There are random very slow rxdrops for certain OpenStack VMs for their
> > network tap interfaces. Please note that this is rxdrop, NOT txdrop.
> >
> > I know we could tune txqueuelen and multi-queue for tap network
> > interface txdrop issue, but is there any known way to tune for this
> > tap network interface rxdrop issue?
> i think a rx drop typically means the vswtich/kernel is droping packets so i think
> any tuneing you applied would have to be on the kernel side.
>
> with that said you can configure the rxqueue lenght and enabel multi queue will also result in
> addtional rx queue so it may help but no i dont know of any one fix for this you will have
> to see what turning work in yoru env for your given traffic profile.
> >
> > Thanks,
> > Hai
> >
>
>



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