Re: [dpdk-dev] About round trip latency with DPDK

[Alex Markuze <alex@weka.io>]

Kai, the latency depends both on what you do and how much you send.
A bigger packet will take longer time to transmit.

Now that thats out of the way I propose you use perf to see how busy
is the cpu and with what.

FYI, ~10us is something that can be achieved with netperf   with a
kernel driver based on interrupts.
The 0.7m latency indicates that something is wrong with your system.

Basically make sure that the cpu is busy with polling only and a small
percent handling the messages.

Hope this helps somehow.

On Wed, Jul 23, 2014 at 10:24 PM, Kai Zhang <zhang.4522@osu.edu> wrote:
> Hello,
>
> I am trying to develop a low-latency application, and I measured the round
> trip latency with DPDK. However I got an average of 650~720 microseconds
> round-trip latency with Intel 82599 10Gbps NIC.
>
> The experiment method is as follows. 2 machines (A and B) are connected
> back-to-back. Machine A embeds a time stamp in the packet and sends to B, B
> (use testpmd or l2fwd) forwards packets back to A immediately (A->B->A),
> and A receives packets and calculates time difference between current time
> and the embedded time stamp. (code :
> https://github.com/kay21s/dpdk/tree/master/examples/recv_send)
>
> I have 3 machines, and performing the above experiment on each pair leads
> to a similar latency. However, previous academic papers report that DPDK
> offers only a few 10 microseconds round trip latency.
>
> What's the round trip latency DPDK is supposed to offer? Have you measured
> it at Intel?
>
> Thanks a lot,
> Kai