the packet delay is too long when I used dpdk i40e NIC sent single packet

[jiangheng]

Hi,
I changed I40E_QUEUE_ITR_INTERVAL_DEFAULT to 10us, latency is significantly lower.
what is the effect of modifying this parameter?

> Hi,
> 
> Could you try to change interval configuration to check if it helps?
> Please refer to i40e_calc_itr_interval function.
> In theory, the lower interval, the lower latency.
> 
> BR,
> Beilei
> 
>> -----Original Message-----
>> From: jiangheng <jiangheng14 at huawei.com>
>> Sent: Wednesday, July 5, 2023 9:33 AM
>> To: Zhang, Yuying <yuying.zhang at intel.com>; Xing, Beilei
>> <beilei.xing at intel.com>
>> Cc: users at dpdk.org
>> Subject: the packet delay is too long when I used dpdk i40e NIC sent single
>> packet
>> 
>> Hi Beilei:
>> we used dpdk implement a user mode tcp protocol stack, and we are testing
>> the delay of a single packet.
>> however, on i40e NIC(XL710), the packet delay is higher than that of the kernel.
>> After some tests, we find that the time consuming may be the pahse when i40e
>> sends packet.(period from rte_eth_tx_burst to packet be sent) The same test is
>> performed on the ixgbe(82599) NIC. the delay is lower than that in kernel.
>> 
>> I used dpdk-21.11 stable version.
>> I tried upgrading the i40e's firmware version to 9.10, but there was no
>> improvement.
>> Any suggestion?
>> Thank you.
>> 
>> 
>> 
>> The following is packet delay statistics of tcpdump:
>> i40e NIC:
>> 410	10.373817	192.168.4.4	192.168.4.5	TCP	64	8877
>> →58312 [ACK] Seq=6511 Ack=9642 Win=1048384 Len=0
>>     10us
>> 411	10.373827	192.168.4.4	192.168.4.5	TCP	94	58312
>> →8877 [PSH, ACK] Seq=9642 Ack=6511 Win=1048512 Len=36
>>     27us
>> 412	10.373854	192.168.4.5	192.168.4.4	TCP	60	8877
>> →58312 [ACK] Seq=6511 Ack=9678 Win=1048320 Len=0
>>     9us
>> 413	10.373863	192.168.4.5	192.168.4.4	TCP	90	58312
>> →8877 [PSH, ACK] Seq=9642 Ack=6511 Win=1048512 Len=36
>>     28us
>> 414	10.373891	192.168.4.4	192.168.4.5	TCP	64	8877
>> →58312 [ACK] Seq=6511 Ack=9678 Win=1048320 Len=0
>>     11us
>> 415	10.373902	192.168.4.4	192.168.4.5	TCP	94	58312
>> →8877 [PSH, ACK] Seq=9678 Ack=6511 Win=1048512 Len=36
>>     28us
>> 416	10.373930	192.168.4.5	192.168.4.4	TCP	60	8877
>> →58312 [ACK] Seq=6511 Ack=9714 Win=1048320 Len=0
>>     11us
>> 417	10.373941	192.168.4.5	192.168.4.4	TCP	90	58312
>> →8877 [PSH, ACK] Seq=9678 Ack=6511 Win=1048512 Len=36
>>     25us
>> 418	10.373967	192.168.4.4	192.168.4.5	TCP	64	8877
>> →58312 [ACK] Seq=6511 Ack=9714 Win=1048320 Len=0
>>     11us
>> 419	10.373978	192.168.4.4	192.168.4.5	TCP	94	58312
>> →8877 [PSH, ACK] Seq=9714 Ack=6511 Win=1048512 Len=36
>>     4us
>> 420	10.373982	192.168.4.5	192.168.4.4	TCP	60	8877
>> →58312 [ACK] Seq=6511 Ack=9750 Win=1048256 Len=0
>> 
>> 
>> ixgbe NIC:
>> 110	13.235208	192.168.4.12	192.168.4.11	TCP	64	8877
>> →58312 [ACK] Seq=6511 Ack=7266 Win=1047808 Len=0
>>     10us
>> 111	13.235218	192.168.4.12	192.168.4.11	TCP	94	58312
>> →8877 [PSH, ACK] Seq=7266 Ack=6511 Win=1048512 Len=36
>>     6us
>> 112	13.235224	192.168.4.11	192.168.4.12	TCP	64	8877
>> →58312 [ACK] Seq=6511 Ack=7302 Win=1047744 Len=0
>>     10us
>> 113	13.235234	192.168.4.11	192.168.4.12	TCP	94	58312
>> →8877 [PSH, ACK] Seq=7266 Ack=6511 Win=1048512 Len=36
>>     6us
>> 114	13.235240	192.168.4.12	192.168.4.11	TCP	64	8877
>> →58312 [ACK] Seq=6511 Ack=7302 Win=1047744 Len=0
>>     11us
>> 115	13.235251	192.168.4.12	192.168.4.11	TCP	94	58312
>> →8877 [PSH, ACK] Seq=7302 Ack=6511 Win=1048512 Len=36
>>     5us
>> 116	13.235256	192.168.4.11	192.168.4.12	TCP	64	8877
>> →58312 [ACK] Seq=6511 Ack=7338 Win=1047744 Len=0
>>     11us
>> 117	13.235267	192.168.4.11	192.168.4.12	TCP	94	58312
>> →8877 [PSH, ACK] Seq=7302 Ack=6511 Win=1048512 Len=36
>>     6us
>> 118	13.235273	192.168.4.12	192.168.4.11	TCP	64	8877
>> →58312 [ACK] Seq=6511 Ack=7338 Win=1047744 Len=0
>>     10us
>> 119	13.235283	192.168.4.12	192.168.4.11	TCP	94	58312
>> →8877 [PSH, ACK] Seq=7338 Ack=6511 Win=1048512 Len=36
>>     6us
>> 120	13.235289	192.168.4.11	192.168.4.12	TCP	64	8877
>> →58312 [ACK] Seq=6511 Ack=7374 Win=1047680 Len=0