rte_eth_tx_burst() always returns 0 in tight loop

[Stephen Hemminger]

On Wed, 6 Jul 2022 09:21:28 +0200
Antonio Di Bacco <a.dibacco.ks at gmail.com> wrote:

> I wonder why calling eth_dev_tx_burst in a tight loop doesn't allow to
> write the packets into the transmit buffer. Only solution I found is
> to include a small delay after the tx_burst that is less than the
> estimated serialization time of the packet in order to be able to
> saturate the ethernet line.
> 
> Anyway I wonder if this is the right approach.
> 
> Thx,
> Antonio.
> 
> On Sun, Jul 3, 2022 at 10:19 PM Gábor LENCSE <lencse at hit.bme.hu> wrote:
> >
> > Dear Antonio,
> >
> > According to my experience, the rte_eth_tx_burst() function reports the
> > packets as "sent" (by a non-zero return value), when they are still in
> > the transmit buffer.
> >
> > (If you are interested in the details, you can see them in Section 3.6.5
> > of this paper: http://www.hit.bme.hu/~lencse/publications/e104-b_2_128.pdf )
> >
> > Therefore, I think that the return value of 0 may mean that
> > rte_eth_tx_burst() can't even commit itself for the future delivery of
> > the packets. I could only guess why. E.g. all its resources have been
> > exhausted.
> >
> > Best regards,
> >
> > Gábor
> >
> >
> > 7/3/2022 5:57 PM keltezéssel, Antonio Di Bacco írta:  
> > > I'm trying to send packets continuously in a  tight loop with a burst
> > > size of 8 and packets are 9600 bytes long.
> > > If I don't insert a delay after the rte_eth_tx_burst it always returns 0.
> > >
> > > What's the explanation of this behaviour ?
> > >
> > > Best regards,
> > > Antonio.  
> >  

Which driver? How did you set the tx_free threshold.
The driver will need to cleanup already transmitted packets.