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

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

Hi Oliver,

> -----Original Message-----
> From: Olivier MATZ [mailto:olivier.matz@6wind.com]
> Sent: Thursday, November 27, 2014 9:11 AM
> To: Ananyev, Konstantin; dev@dpdk.org
> Cc: Walukiewicz, Miroslaw; Liu, Jijiang; Liu, Yong; jigsaw@gmail.com; Richardson, Bruce
> Subject: Re: [PATCH v4 08/13] testpmd: rework csum forward engine
> 
> 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

My initial thought:
It tells the NIC that it is an IPV4 packet for which it has to compute checksum.

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

It tells the NIC that it is an IPV4 packet for which it shouldn't compute checksum.

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

Yes.

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

Yes, it could be done in both ways:
either all 3 flags are mutually exclusive 
or first two and third one are mutually exclusive.

Current i40e PMD  seems to work correctly with the second way too.

Though the second way implies a specific order for PMD to check flags.
Something like:
 if (ol_flags & PKT_TX_IP_CKSUM) {..} else if (ol_flags & PKT_TX_IPV4) {...} else ...
would work correctly.
But:
if (ol_flags & PKT_TX_IPV4) {...} else if (ol_flags & PKT_TX_IP_CKSUM) {..} else
wouldn't.

> 
> >> +/* 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.

Function: process_outer_cksums(), line 273:

if (udp_hdr->dgram_cksum != 0) {
                udp_hdr->dgram_cksum = 0;
                if ((testpmd_ol_flags & TESTPMD_TX_OFFLOAD_VXLAN_CKSUM) == 0) {   /* <-- THAT ONE. */
                        if (outer_ethertype == _htons(ETHER_TYPE_IPv4))

I think it is no need for it there.

> 
> I'll check how Jijiang fixed the issue.
> 
> Regards,
> Olivier