Re: [dpdk-dev] [PATCH] app/testpmd: Document what the application does.

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 9/10/2021 6:57 PM, Ben Pfaff wrote:
> I could not find anything in the documentation that says what
> testpmd does.  This should save other people time trying to
> figure that out in the future.
> 
> Signed-off-by: Ben Pfaff <blp@ovn.org>
> ---
>  doc/guides/testpmd_app_ug/run_app.rst | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/doc/guides/testpmd_app_ug/run_app.rst b/doc/guides/testpmd_app_ug/run_app.rst
> index 6061674239..7c3406f72b 100644
> --- a/doc/guides/testpmd_app_ug/run_app.rst
> +++ b/doc/guides/testpmd_app_ug/run_app.rst
> @@ -15,6 +15,12 @@ a list of available EAL command-line options.
>  Testpmd Command-line Options
>  ----------------------------
>  
> +By default, testpmd receives packets on each configured port and
> +forwards the received packets to its paired port.  Ports 0 and 1 are
> +paired, as are ports 2 and 3, and so on.  With an odd number of ports,
> +the last port is paired with itself: packets received on the port are
> +sent back out on the same port.
Hi Ben,

testpmd has the concept of 'forwarding engine' (struct fwd_engine), which is
decoupled from testpmd logic and can be changed in the runtime. What you
described above is the 'io' (default) forwarding engine.
There are forwarding engines like 'flowgen' that generates and send L3 packets,
so behaves like a very simple packet generator, etc...

And even for the 'io' forwarding engine, the paired port description above is
controlled by "--port-topology=<paired|chained|loop>", so for example if the
'chained' topology is selected, packets will be forwarded as 0 -> 1 -> 2 -> 3 ..


Overall, I understand the intention to briefly describe the testpmd, but I think
it is not correct to reduce the description to packet forwarding, although that
is an important function of testpmd, it is not only function and testpmd does
much more, it has many control path functions.

Cheers,
ferruh


> +
>  The following are the command-line options for the testpmd applications.
>  They must be separated from the EAL options, shown in the previous section, with a ``--`` separator:
>  
>