Re: [PATCH v3] app/testpmd: add parameter to start forwarding TX first

[Thomas Monjalon <thomas@monjalon.net>]

20/06/2017 11:22, Bruce Richardson:
> On Mon, Jun 19, 2017 at 11:12:53PM +0200, Thomas Monjalon wrote:
> > 15/06/2017 14:05, De Lara Guarch, Pablo:
> > > > Add parameter to start forwarding sending first
> > > > a burst of packets, which is useful when testing
> > > > a loopback connection.
> > > > 
> > > > This was already implemented as an internal command,
> > > > but adding it as a parameter is interesting, as it
> > > > allows the user to test a loopback connection without
> > > > entering in the internal command line.
> > > > 
> > > > Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
> > > > ---
> > > > --- a/doc/guides/testpmd_app_ug/run_app.rst
> > > > +++ b/doc/guides/testpmd_app_ug/run_app.rst
> > > > @@ -188,6 +188,14 @@ The commandline options are:
> > > > 
> > > >      Start forwarding on initialization.
> > > > 
> > > > +*   ``--tx-first``
> > > > +
> > > > +    Start forwarding, after sending a burst of packets first.
> > > > +
> > > > +.. Note::
> > > > +
> > > > +   This flag should be only used in non-interactive mode.
> > 
> > I don't really understand the benefit of this option.
> > Why is it better than
> > 	echo start tx_first | testpmd -i
> > ?
> 
> The one big difference I see is normal vs abnormal termination. With the
> echo command you suggest, the only way to terminate testpmd is to kill
> it via signal. With the extra cmdline option, it will cleanly exit via
> enter as with non-interactive mode right now. Not a huge difference, but
> I think having the extra argument to enable tx-first is useful.

I do not see a big difference between "enter" and "ctrl+c".

I think it is more flexible to pipe commands instead of options.
We could combine the proposed options --tx-first and -T into this command:
( echo 'start tx_first' ; while true ; do echo 'show port stats all' ; sleep 1 ; done ) | testpmd -i 

It is even possible to add more actions in the loop, so it is less
limited than the -T options.

It is a matter of deciding whether we prefer to implement more restricted
options or leverage the shell to freely program non-interactive testpmd.