[dpdk-dev] Fwd: high latency detected in IP pipeline example

James Huang jamsphon at gmail.com
Tue Feb 18 00:10:35 CET 2020

Yes, I experienced similar issue in my application. In a short answer, set
the swqs write burst value to 1 may reduce the latency significantly. The
default write burst value is 32.

On Mon., Feb. 17, 2020, 8:41 a.m. Victor Huertas <vhuertas at gmail.com> wrote:

> Hi all,
> I am developing my own DPDK application basing it in the dpdk-stable
> ip_pipeline example.
> At this moment I am using the 17.11 LTS version of DPDK and I amb observing
> some extrange behaviour. Maybe it is an old issue that can be solved
> quickly so I would appreciate it if some expert can shade a light on this.
> The ip_pipeline example allows you to develop Pipelines that perform
> specific packet processing functions (ROUTING, FLOW_CLASSIFYING, etc...).
> The thing is that I am extending some of this pipelines with my own.
> However I want to take advantage of the built-in ip_pipeline capability of
> arbitrarily assigning the logical core where the pipeline (f_run()
> function) must be executed so that i can adapt the packet processing power
> to the amount of the number of cores available.
> Taking this into account I have observed something strange. I show you this
> simple example below.
> Case 1:
> [PIPELINE 0 MASTER core =0]
> [PIPELINE 1 core=1] --- SWQ1--->[PIPELINE 2 core=2] -----SWQ2---->
> [PIPELINE 3 core=3]
> Case 2:
> [PIPELINE 0 MASTER core =0]
> [PIPELINE 1 core=1] --- SWQ1--->[PIPELINE 2 core=1] -----SWQ2---->
> [PIPELINE 3 core=1]
> I send a ping between two hosts connected at both sides of the pipeline
> model which allows these pings to cross all the pipelines (from 1 to 3).
> What I observe in Case 1 (each pipeline has its own thread in different
> core) is that the reported RTT is less than 1 ms, whereas in Case 2 (all
> pipelines except MASTER are run in the same thread) is 20 ms. Furthermore,
> in Case 2, if I increase a lot (hundreds of Mbps) the packet rate this RTT
> decreases to 3 or 4 ms.
> Has somebody observed this behaviour in the past? Can it be solved somehow?
> Thanks a lot for your attention
> --
> Victor
> --
> Victor

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