[dpdk-dev] [PATCH v3] app/testpmd: add parameter to start forwarding TX first

[Van Haaren, Harry]

> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Gaëtan Rivet
> Sent: Tuesday, June 20, 2017 11:19 AM
> To: Thomas Monjalon <thomas at monjalon.net>
> Cc: Richardson, Bruce <bruce.richardson at intel.com>; De Lara Guarch, Pablo
> <pablo.de.lara.guarch at intel.com>; dev at dpdk.org; Wu, Jingjing <jingjing.wu at intel.com>
> Subject: Re: [dpdk-dev] [PATCH v3] app/testpmd: add parameter to start forwarding TX first
> 
> On Tue, Jun 20, 2017 at 11:58:54AM +0200, Thomas Monjalon wrote:
> > 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 at 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.
> 
> Side note, one can:
> 
> (trap 'echo quit' SIGUSR1; echo 'start'; while true; do sleep 1; done) |testpmd -i &
> 
> and issue a SIGUSR1 to the subshell to cleanly quit testpmd.
> Or:
> 
> (trap 'echo show port stats all' SIGUSR1; \
>  trap 'echo quit' SIGUSR2; \
>  echo 'start'; \
>  while true; do :; done) |\
> testpmd -i &
> 
> It's a little contrived, but it does the job and is easy enough to put
> in scripts.
> 
> For automated testing, what I did was open a pipe to testpmd to issue
> commands from wherever, allowing to keep testpmd running in the
> background and dispatch commands when needed from other terminals. No
> need to issue signals at all then.

In an expert-user automated testing environment this is a solution yes..


> > 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.


Lets keep in mind the beginner users, who probably don't have a traffic generator machine, perhaps just 2 ports and a loopback cable. IMO running   ./testpmd -- --tx-first   is the easiest way to learn to run traffic using testpmd, instead of various shell tricks to work-around a missing CLI flag?

A +1 from me to add   --tx-first  to the CLI, -Harry