Re: [dpdk-dev] roundtrip delay

["Jayakumar, Muthurajan" <muthurajan.jayakumar@intel.com>]

Please kindly refer recent thread titled "DPDK Latency Issue" on similar topic. Below copied and pasted Jeff Shaw reply on that thread.

Hello,

> I measured a roundtrip latency (using Spirent traffic generator) of sending 64B packets over a 10GbE to DPDK, and DPDK does nothing but simply forward back to the incoming port (l3fwd without any lookup code, i.e., dstport = port_id).
> However, to my surprise, the average latency was around 150 usec. (The packet drop rate was only 0.001%, i.e., 283 packets/sec dropped) Another test I did was to measure the latency due to sending only a single 64B packet, and the latency I measured is ranging anywhere from 40 usec to 100 usec.

40-100usec seems very high.
The l3fwd application does some internal buffering before transmitting the packets.  It buffers either 32 packets, or waits up to 100us (hash-defined as BURST_TX_DRAIN_US), whichever comes first.
Try either removing this timeout, or sending a burst of 32 packets at time.  Or you could try with testpmd, which should have reasonably low latency out of the box.

There is also a section in the Release Notes (8.6 How can I tune my network application to achieve lower latency?) which provides some pointers for getting lower latency if you are willing to give up top-rate throughput.

Thanks,
Jeff

-----Original Message-----
From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Helmut Sim
Sent: Sunday, May 25, 2014 7:55 AM
To: dev@dpdk.org
Subject: [dpdk-dev] roundtrip delay

Hi,

what is the way to optimize the round trip delay of a packet?
i.e. receiving a packet and then resending it back to the network in a minimal time, assuming the rx and tx threads are on a continuous loop of rx/tx.

Thanks,