-----Original Message-----
From: Stephen Hemminger <stephen@networkplumber.org>
Sent: Wednesday, September 15, 2021 12:44 AM
To: Ananyev, Konstantin <redacted>
Cc: Usama Nadeem <redacted>; 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" [off-list ref] wrote:

quoted

quoted

From: usamanadeem321 <redacted>

Checks if IPV4, UDP and TCP Checksum offloads are available.
If not available, prints a warning message.

Bugzilla ID: 545
Signed-off-by: usamanadeem321 <redacted>
---
 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."

quoted

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.