Re: [dpdk-dev] [PATCH v2] Warns if IPv4, UDP or TCP checksum offload not available

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Wednesday, September 15, 2021 12:44 AM
> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> Cc: Usama Nadeem <usama.nadeem@emumba.com>; thomas@monjalon.net; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] Warns if IPv4, UDP or TCP checksum offload not available
> 
> On Tue, 14 Sep 2021 22:22:04 +0000
> "Ananyev, Konstantin" <konstantin.ananyev@intel.com> wrote:
> 
> > >
> > > From: usamanadeem321 <usama.nadeem@emumba.com>
> > >
> > > Checks if IPV4, UDP and TCP Checksum offloads are available.
> > > If not available, prints a warning message.
> > >
> > > Bugzilla ID: 545
> > > Signed-off-by: usamanadeem321 <usama.nadeem@emumba.com>
> > > ---
> > >  examples/l3fwd/main.c | 22 +++++++++++++++++++++-
> > >  1 file changed, 21 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/examples/l3fwd/main.c b/examples/l3fwd/main.c
> > > index 00ac267af1..ae62bc570d 100644
> > > --- a/examples/l3fwd/main.c
> > > +++ b/examples/l3fwd/main.c
> > > @@ -123,7 +123,6 @@ static struct rte_eth_conf port_conf = {
> > >  		.mq_mode = ETH_MQ_RX_RSS,
> > >  		.max_rx_pkt_len = RTE_ETHER_MAX_LEN,
> > >  		.split_hdr_size = 0,
> > > -		.offloads = DEV_RX_OFFLOAD_CHECKSUM,
> > >  	},
> > >  	.rx_adv_conf = {
> > >  		.rss_conf = {
> > > @@ -1039,6 +1038,27 @@ l3fwd_poll_resource_setup(void)
> > >  			local_port_conf.txmode.offloads |=
> > >  				DEV_TX_OFFLOAD_MBUF_FAST_FREE;
> > >
> > > +		if (dev_info.rx_offload_capa & DEV_RX_OFFLOAD_IPV4_CKSUM)
> > > +			local_port_conf.rxmode.offloads |=
> > > +			 DEV_RX_OFFLOAD_IPV4_CKSUM;
> > > +		else {
> > > +			printf("WARNING: IPV4 Checksum offload not available.\n");
> > > +		}
> > > +
> > > +		if (dev_info.rx_offload_capa & DEV_RX_OFFLOAD_UDP_CKSUM)
> > > +			local_port_conf.rxmode.offloads |=
> > > +			DEV_RX_OFFLOAD_UDP_CKSUM;
> > > +
> > > +		else
> > > +			printf("WARNING: UDP Checksum offload not available.\n");
> > > +
> > > +		if (dev_info.rx_offload_capa & DEV_RX_OFFLOAD_TCP_CKSUM)
> > > +			local_port_conf.rxmode.offloads |=
> > > +			DEV_RX_OFFLOAD_TCP_CKSUM;
> > > +
> > > +		else
> > > +			printf("WARNING: TCP Checksum offload not available.\n");
> > > +
> >
> > Sorry, but I didn't get the logic:
> > Application expects some offloads to be supported by HW.
> 
> The application is expecting more offloads than is necessary for basic
> IP level forwarding which is all the example is documented to do.
> 
>   "The application performs L3 forwarding."
> 
> > You add the code that checks for offloads, but if they are not supported just prints warning
> > and continues, as if everything is ok. Doesn't look like correct behaviour to me.
> > I think, it should either terminate with error message or be prepared to work properly
> > on HW without these offloads (check cksums in SW if necessary).
> > In fact I don't see what was wrong with original behaviour, one thing that probably
> > was missing - more descriptive error message.
> 
> It is not a problem with your patch, it is fine.
> 
> It is a problem in how l3fwd has grown and changed and no longer really what
> was intended in the original version. There is no reason that the application
> should be looking at L4 data. In fact, it shouldn't care if it gets TCP, UDP, SCP or DCCP;
> but the application now depends on ptype.
> 
> It should be possible to do L3 forwarding independent of packet type.
> The application only needs to look at Ether type and do IPv4 or IPv6 based on that.
> 

As I remember l3fwd cares about L4 headers (chan cksums) because it can do FWD decisions
based on 5-tuple (exact-macth mode).
I presume that's the reason L4 cksum offloads was enabled at first place.
For LPM/FIB I believe ipv4 cksum check should be sufficient.
If we believe that some offloads are excessive,
then I think right way is to simply remove them
(with updating docs and source in a proper way etc.).
Just printing warnings and continuing seems wrong to me.