Re: (AWS ENA NIC) queued v. out packets reported by any of the DPDK stats functions

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 15 Mar 2022 15:28:55 -0400
fwefew 4t4tg <7532yahoo@gmail.com> wrote:

> On DPDK head commit (917229) I have a simple program creating two TXQs each
> sending 15000 IPV4 UDP packets.
> 
> As far as I can see there are no errors anymore. I have looked. I burst TX
> them in blocks of 15; rte_eth_tx_burst always returns 15.
> 
> The lcores are launched with rte_eal_mp_remote_launch, and main() blocks
> until rte_eal_mp_wait_lcore() returns.
> 
> However, at any time after rte_eal_mp_wait_lcore returns showing the number
> of out packets as per rte_eth_stats_get or xstats per rte_eth_xstats_get I
> see two things:
> 
> - the reported number of queued packets per TXQ is always 15000
> - the number of out packets or "good packets" is close to 15000*2 but never
> 30000
> 
> It appears like the TXQs still have work in-queue even after the lcore's
> thread returns and rte_eal_mp_wait_lcore returns. I've tried to
> rte_eth_tx_done_cleanup and/or rte_eth_dev_tx_queue_stop before I get the
> stats. That doesn't seem to help.
> 
> The TXQ config is default except for checksum offloads:
> 
> 000000.336378246 DEBUG reinvent_dpdk_initaws.cpp:1341 TXQ conf:
> {"tx_thresh": { "pthresh": 0, "hthresh": 0, "wthresh": 0 }, "tx_rs_thresh":
> 0, "tx_free_thresh": 0, "tx_deferred_start": 0, "tx_offloads": 00008006, }
> 
> Is this expected behavior? I've look through code; I haven't seen clear
> signs of a TXQ oriented lcore flushed or waiting for the output queue to be
> actually written onto the wire before exiting.
> 

No part of lcore_wait is related directly to TxQ. 
The TxQ runs asynchronously. If you have to check if packet was sent, the
you would need to use rte_eth_tx_descriptor_status().

But not all hardware supports this API; AWS ENA does not.