Re: [PATCH] net: orphan queued skbs if device tx can stall

From: Herbert Xu
Date: Mon Apr 09 2012 - 04:29:25 EST


On Mon, Apr 09, 2012 at 10:39:54AM +0300, Michael S. Tsirkin wrote:
> On Mon, Apr 09, 2012 at 03:33:54PM +0800, Herbert Xu wrote:
> > On Mon, Apr 09, 2012 at 10:28:49AM +0300, Michael S. Tsirkin wrote:
> > >
> > > > 1) Doesn't this break local UDP push-back?
> > >
> > > What is meant by UDP pushback here? Two tap
> > > devices communicating by UDP packets locally?
> > > This was always broken, see below.
> >
> > I mean push-back from UDP transmission to the physical NIC.
> >
> > Your patch breaks that
>
> I think there's some misunderstanding. pushback is only disabled
> for destinations that set IFF_TX_CAN_STALL. I expect that
> no physical NICs set this flag - only tun and possibly
> other userspace-controlled devices in the future.

I'm talking about an app running in the guest transmitting UDP
to the physical NIC via virtio/vhost. This will break with your
patch.

Cheers,
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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