Re: [dpdk-dev] [PATCH v6 2/2] testpmd: add mode 4 support v6

["Jastrzebski, MichalX K" <michalx.k.jastrzebski@intel.com>]

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> Sent: Wednesday, November 26, 2014 2:31 PM
> To: Wodkowski, PawelX
> Cc: Jastrzebski, MichalX K; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v6 2/2] testpmd: add mode 4 support v6
> 
> 2014-11-26 13:00, Wodkowski, PawelX:
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas Monjalon
> > > 2014-11-26 11:17, Michal Jastrzebski:
> > > > From: Pawel Wodkowski <pawelx.wodkowski@intel.com>
> > > > --- a/app/test-pmd/csumonly.c
> > > > +++ b/app/test-pmd/csumonly.c
> > > > @@ -254,8 +254,17 @@ pkt_burst_checksum_forward(struct
> fwd_stream *fs)
> > > >  	 */
> > > >  	nb_rx = rte_eth_rx_burst(fs->rx_port, fs->rx_queue, pkts_burst,
> > > >  				 nb_pkt_per_burst);
> > > > +#ifndef RTE_LIBRTE_PMD_BOND
> > > >  	if (unlikely(nb_rx == 0))
> > > >  		return;
> > > > +#else
> > > > +	if (unlikely(nb_rx == 0 && (fs->forward_timeout == 0 ||
> > > > +			fs->next_forward_time > rte_rdtsc())))
> > > > +		return;
> > > > +
> > > > +	if (fs->forward_timeout != 0)
> > > > +		fs->next_forward_time = rte_rdtsc() + fs->forward_timeout;
> > > > +#endif
> > >
> > > I don't understand why you need to make such change for bonding,
> > > and there is no comment to explain.
> > > Bonding should be a PMD like any other and shouldn't require such
> change.
> > > I don't know mode 4 but it seems there is a design problem here.
> > >
> >
> > It is an implication of requirement that was formed on beginning of
> bonding
> > implementation - bonded interface should be transparent to user app. But
> this
> > requirement in is in collision with mode 4. It need to periodically receive
> and
> > transmit frames (LACP and marker) that are not passed to user app but
> > processed/produced in background. If this will not happen in at least 10
> times
> > per second mode 4 will not work.
> >
> > Most of (all?) user applications do RX/TX more often than 10 times per
> second,
> > so this will have neglectable impact to those apps (it will have to check this
> > 100ms maximum interval of rx/tx as I did in code you pointed).
> >
> > We had discussed all options with Declan and Bruce, and this seems to be
> the
> > most transparent way to implement mode 4 without using any kind of
> locking
> > inside library.
> 
> So you agree there is a design problem and you were initially trying to push it
> without raising the problem in the hope that nobody will see it?
No, we didn't want to hide anything. 
> It's really not the good way to work in an Open Source project.
> 
> Is there any comment in the API to explain this new constraint?
No, we haven't put in the code a straight comment. I wrote about it in cover letter in v6
and there is also show_warnings function in patch 1/2 which will print a warning to the 
application.
> Do you think we can change how Rx/Tx works in DPDK to integrate this
> feature?
> 
> Actually, I think these bonding features should be implemented in a layer on
> top of DPDK. It's not the DPDK responsibility to make some protocol
> processing.
> Bonding was integrated with the promise that it's transparent and really
> close
> to the hardware ports.
> 
> Today I see we clearly need a discussion to know what should be
> implemented
> in DPDK. Which protocol layer is the limit?
> I explained my point of view but the decision belongs to the whole
> community.
> 
> --
> Thomas