[dpdk-dev] can eth_igb_xmit_pkts called with len 0 affect transmission?

[Lu, Wenzhuo]

Hi Ciprian,

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of ciprian.barbu
> Sent: Thursday, July 23, 2015 11:20 PM
> To: dev at dpdk.org
> Subject: Re: [dpdk-dev] can eth_igb_xmit_pkts called with len 0 affect
> transmission?
> 
> Anyone?
> 
> On 17.07.2015 16:48, ciprian.barbu wrote:
> > Hi,
> >
> > I'm seeing a strange behavior when calling rte_eth_tx_burst with len
> > == 0. I'll explain the reason for this situation further bellow. But
> > what I'm seeing is that after doing this call my application keeps
> > returning from eth_igb_xmit_pkts here, even when len > 0:
> > http://dpdk.org/browse/dpdk/tree/lib/librte_pmd_e1000/igb_rxtx.c?h=rel
> > eases#n476
Don’t understand what the len means? The packet length? 
According to where the code returns, seems the queue is not initialized correctly.
I saw you used odp-dpdk. Sorry, I'm not familiar with it. Why not try dpdk examples,
and check if the behavior is same?

> >
> >
> > I can't really explain myself this behavior, I don't understand very
> > well what the nic does once it receives buffers in its rings, but to
> > me it looks like calling rte_eth_tx_burst with len 0 has this effect.
> >
> > What I'm using in my tests is the linaro odp-dpdk implementation and
> > the odp_l2fwd example. The odp-dpdk implementation makes this call to
> > try and make the pmd to flush the tx queue in case there are no more
> > free buffers in the pool, but this was only verified for ixgbe 82599
> > cards, for igb the packets are not actually flushed until the tail
> > circles back the whole length of the queue. I'm pretty much the only
> > one (that I know
> > of) that uses odp with 1G igb i350 cards and see this issue.
> >
> > Can anyone explain whether I'm getting this right and there could be
> > side effects to calling eth_igb_xmit_pkts with len 0?
> >
> > Thank you,
> > /Ciprian