Re: [dpdk-dev] [PATCH v4 08/13] testpmd: rework csum forward engine

[Olivier MATZ <olivier.matz@6wind.com>]

Hi Konstantin,

On 11/26/2014 09:02 PM, Ananyev, Konstantin wrote:
>> +/* if possible, calculate the checksum of a packet in hw or sw,
>> + * depending on the testpmd command line configuration */
>> +static uint64_t
>> +process_inner_cksums(void *l3_hdr, uint16_t ethertype, uint16_t l3_len,
>> +	uint8_t l4_proto, uint16_t testpmd_ol_flags)
>> +{
>> +	struct ipv4_hdr *ipv4_hdr = l3_hdr;
>> +	struct udp_hdr *udp_hdr;
>> +	struct tcp_hdr *tcp_hdr;
>> +	struct sctp_hdr *sctp_hdr;
>> +	uint64_t ol_flags = 0;
>> +
>> +	if (ethertype == _htons(ETHER_TYPE_IPv4)) {
>> +		ipv4_hdr = l3_hdr;
>> +		ipv4_hdr->hdr_checksum = 0;
>> +
>> +		if (testpmd_ol_flags & TESTPMD_TX_OFFLOAD_IP_CKSUM)
>> +			ol_flags |= PKT_TX_IP_CKSUM;
>> +		else
>> +			ipv4_hdr->hdr_checksum = get_ipv4_cksum(ipv4_hdr);
>> +
>> +		ol_flags |= PKT_TX_IPV4;
>
> Flags PKT_TX_IP_CKSUM, PKT_TX_IPV4, PKT_TX_IPV6 are all mutually exclusive.
> So it should be, I think:
>
> if (testpmd_ol_flags & TESTPMD_TX_OFFLOAD_IP_CKSUM) {
>              ol_flags |= PKT_TX_IP_CKSUM;
>   } else {
>               ipv4_hdr->hdr_checksum = get_ipv4_cksum(ipv4_hdr);
>               ol_flags |= PKT_TX_IPV4;
> }

It seems normal that PKT_TX_IPV4 are PKT_TX_IPV6 exclusive, but do you
mean that PKT_TX_IP_CKSUM and PKT_TX_IPV4 are exclusive too? It looks
strange to me.

My understanding of the meaning of the flags is:

   - PKT_TX_IP_CKSUM: tell the NIC to compute IP cksum

   - PKT_TX_IPV4: tell the NIC it's an IPv4 packet. Required for L4
     checksum offload or TSO.

   - PKT_TX_IPV6: tell the NIC it's an IPv6 packet. Required for L4
     checksum offload or TSO.

If it's a i40e driver requirement, don't you think it's better to change
the driver?

>> +/* Calculate the checksum of outer header (only vxlan is supported,
>> + * meaning IP + UDP). The caller already checked that it's a vxlan
>> + * packet */
>> +static uint64_t
>> +process_outer_cksums(void *outer_l3_hdr, uint16_t outer_ethertype,
>> +	uint16_t outer_l3_len, uint16_t testpmd_ol_flags)
>> +{
>> +	struct ipv4_hdr *ipv4_hdr = outer_l3_hdr;
>> +	struct ipv6_hdr *ipv6_hdr = outer_l3_hdr;
>> +	struct udp_hdr *udp_hdr;
>> +	uint64_t ol_flags = 0;
>> +
>> +	if (testpmd_ol_flags & TESTPMD_TX_OFFLOAD_VXLAN_CKSUM)
>> +		ol_flags |= PKT_TX_VXLAN_CKSUM;
>> +
>> +	if (outer_ethertype == _htons(ETHER_TYPE_IPv4)) {
>> +		ipv4_hdr->hdr_checksum = 0;
>> +
>> +		if ((testpmd_ol_flags & TESTPMD_TX_OFFLOAD_VXLAN_CKSUM) == 0)
>> +			ipv4_hdr->hdr_checksum = get_ipv4_cksum(ipv4_hdr);
>> +	}
>> +
>> +	udp_hdr = (struct udp_hdr *)((char *)outer_l3_hdr + outer_l3_len);
>> +	/* do not recalculate udp cksum if it was 0 */
>> +	if (udp_hdr->dgram_cksum != 0) {
>> +		udp_hdr->dgram_cksum = 0;
>> +		if ((testpmd_ol_flags & TESTPMD_TX_OFFLOAD_VXLAN_CKSUM) == 0) {
>
> In fact, FVL is not able to do HW caclualtion for outer L4, only outer IPV4 cksum is supported.
> So no need for:
> if (testpmd_ol_flags & TESTPMD_TX_OFFLOAD_UDP_CKSUM) {
> above.
> And yes, if user will select to calculate inner checksums by HW - outer UDP checksum might be invalid anyway.

I may have misunderstood how vxlan works, so I agree this code is
probably wrong. However, I don't find the line you are quoting in
the function above.

I'll check how Jijiang fixed the issue.

Regards,
Olivier