* Re: [dpdk-users] Invalid TCP/UDP checksum for IPV4 packets
[not found] <CADF714Y-eLGjjV3CLmGNvE=fu9YKh7EeZspMK6WfyP2hU3qR2A@mail.gmail.com>
@ 2017-06-07 14:39 ` Thomas Monjalon
0 siblings, 0 replies; only message in thread
From: Thomas Monjalon @ 2017-06-07 14:39 UTC (permalink / raw)
To: Julien Castets; +Cc: users, dev
Hi,
31/05/2017 10:16, Julien Castets:
> I had a running application on DPDK 2.2.0 which offloads IP/TCP/UDP
> checksums to the NIC. A few days ago, I started the migration to 17.02
> and started to see invalid TCP/UDP checksum.
>
> I called the new API rte_eth_tx_prepare() but checksums were still invalid.
>
> After digging for a few hours in DPDK source code, I discovered the
> flag PKT_TX_IPV4 needs to be set in ol_flags.
>
> Basically, the function rte_net_intel_cksum_flags_prepare of rte_net.h
> (http://dpdk.org/doc/api/rte__net_8h_source.html) does the following:
>
> if (offload TCP checksum flag is set) {
> if (PKT_TX_IPV4 in ol_flags) {
> // compute ipv4 checksum
> }
> else {
> // compute ipv6 checksum
> }
> }
>
> Because I didn't set PKT_TX_IPV4 in ol_flags, I was going into the
> "else" clause and the checksum was computed as if my packet was an
> IPV6 packet.
>
> Don't you think it would be preferable to assert instead of
> considering a non-explicitely-declared-IPV4-packet as being an IPV6
> packet?
Yes, you're right.
I think we were avoiding wasting 1 cycle here.
Usability was the cost for best performance.
A good trade-off may be to use RTE_ASSERT which will be triggered only
in debug mode.
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