[PATCH v1 5/5] examples/l3fwd: enable direct rearm mode

[Honnappa Nagarahalli]

<snip>

> 
> > From: Feifei Wang [mailto:feifei.wang2 at arm.com]
> > Sent: Wednesday, 20 April 2022 10.17
> >
> > Enable direct rearm mode. The mapping is decided in the data plane
> > based on the first packet received.
> 
> I usually don't care much about l3fwd, but putting configuration changes in the
> fast path is just wrong!
I would say it depends. In this case the cycles consumed by the API are very less and configuration data is very small and is already in the cache as PMD has accessed the same data structure. 

If the configuration needs more cycles than a typical (depending on the application) data plane packet processing needs or brings in enormous amount of data in to the cache, it should not be done on the data plane.

> 
> Also, l3fwd is often used for benchmarking, and this small piece of code in the
> fast path will affect benchmark results (although only very little).
We do not see any impact on the performance numbers. The reason for putting in the data plane was it covers wider use case in this L3fwd application. If the app were to be simple, the configuration could be done from the control plane. Unfortunately, the performance of L3fwd application matters.

> 
> Please move it out of the fast path.