Hi Lu, Thank you for getting back to me.
On 24.07.2015 05:49, Lu, Wenzhuo wrote: > 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? Sorry about this, failure to communicate :) I meant to say nb_pkts = 0 > According to where the code returns, seems the queue is not initialized > correctly. The queue should have been initialized ok, I'm able to several millions of packets before getting stuck. It's only after I make a rte_eth_tx_burst call with nb_pkts = 0 that I get stuck in that return. Looking at the source code, the function will only do: rte_wmb(); E1000_PCI_REG_WRITE(txq->tdt_reg_addr, tx_id); The barrier should be harmless, so I'm thinking that writing that register without sending any packets causes this behavior. > 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? Of course, I tried the DPDK l2fwd example, that's how I managed to find the difference between odp_l2fwd and DPDK l2fwd. After I removed the piece of code that was calling rte_eth_tx_burst with nb_pkts 0 it started behaving the same as DPDK l2fwd. I suppose I could also modify l2fwd to make this call and see it it gets stuck too. > >>> >>> >>> 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
