[dpdk-dev] [PATCH v5 2/3] mbuf:add three TX ol_flags and repalce PKT_TX_VXLAN_CKSUM

[Liu, Jijiang]

Hi Helin,

> -----Original Message-----
> From: Zhang, Helin
> Sent: Thursday, December 4, 2014 2:52 PM
> To: Olivier MATZ; Ananyev, Konstantin; Liu, Jijiang; dev at dpdk.org
> Subject: RE: [dpdk-dev] [PATCH v5 2/3] mbuf:add three TX ol_flags and repalce
> PKT_TX_VXLAN_CKSUM
> 
> 
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Olivier MATZ
> > Sent: Wednesday, December 3, 2014 10:42 PM
> > To: Ananyev, Konstantin; Liu, Jijiang; dev at dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH v5 2/3] mbuf:add three TX ol_flags and
> > repalce PKT_TX_VXLAN_CKSUM
> >
> > Hi Konstantin,
> >
> > On 12/03/2014 01:59 PM, Ananyev, Konstantin wrote:
> > >> I still think having a flag IPV4 + another flag IP_CHECKSUM is not
> > >> appropriate.
> > >
> > > Sorry, didn't get you here.
> > > Are you talking about our discussion should PKT_TX_IP_CKSUM and
> > PKT_TX_IPV4 be mutually exclusive or not?
> >
> > Yes
> >
> > >> I though Konstantin agreed on other flags, but I may have
> > >> misunderstood:
> > >>
> > >> http://dpdk.org/ml/archives/dev/2014-November/009070.html
> > >
> > > In that mail, I was talking about my suggestion to make
> > > PKT_TX_IP_CKSUM,
> > PKT_TX_IPV4 and PKT_TX_IPV6 to occupy 2 bits.
> > > Something like:
> > > #define	PKT_TX_IP_CKSUM	(1 << X)
> > > #define	PKT_TX_IPV6		(2 << X)
> > > #define 	PKT_TX_IPV4		(3 << X)
> > >
> > > "Even better, if we can squeeze these 3 flags into 2 bits.
> > > Would save us 2 bits, plus might be handy, as in the PMD you can do:
> > >
> > > switch (ol_flags & TX_L3_MASK) {
> > >      case TX_IPV4:
> > >         ...
> > >         break;
> > >      case TX_IPV6:
> > >         ...
> > >         break;
> > >      case TX_IP_CKSUM:
> > >         ...
> > >         break;
> > > }"
> > >
> > > As you pointed out, it will break backward compatibility.
> > > I agreed with that and self-NACKed it.
> >
> > ok, so we are back between:
> >
> > 1/ (Jijiang's patch)
> > PKT_TX_IP_CKSUM  /* packet is IPv4, and we want hw cksum */
> > PKT_TX_IPV6      /* packet is IPv6 */
> > PKT_TX_IPV4      /* packet is IPv4, and we don't want hw cksum */
> >
> > with PKT_TX_IP_CKSUM and PKT_TX_IPV4 exclusive
> >
> > and
> >
> > 2/
> > PKT_TX_IP_CKSUM  /* we want hw IP cksum */
> > PKT_TX_IPV6      /* packet is IPv6 */
> > PKT_TX_IPV4      /* packet is IPv4 */
> There is another bit flag named 'PKT_TX_IPV4_CSUM' which uses the same bit of
> 'PKT_TX_IP_CSUM'. It is for identifying if ipv4 hardware checksum offload is
> needed or not.
> It seems that we do not need 'PKT_TX_IPV6_CSUM'.
> 'PKT_TX_IPV4' and 'PKT_TX_IPV6' just indicates its packet type, and I guess other
> features should not be contained in it, according to its name.
> 
> So here I got the option 3:
> PKT_TX_IPV4_CKSUM  /* we want hw IPv4 cksum */
> PKT_TX_IPV6      /* packet is IPv6 */
> PKT_TX_IPV4      /* packet is IPv4 */

In TX side,  if just tell driver/HW this is a IPV4 packet , and don't tell  driver/HW whether TX checksum  or other offload  is required or not , the flag is senseless,  and hardware will not do any offload.

The flag is not used in igb/ixgbe codes, which is just used in i40e codes, and set this bit(IPv4 packet with no IP checksum offload) in i40e driver.
...
	} else if (ol_flags & PKT_TX_IPV4) {
		*td_cmd |= I40E_TX_DESC_CMD_IIPT_IPV4;
...
		

> >
> > with PKT_TX_IP_CKSUM implies PKT_TX_IPV4
> >
> >
> > Solution 2/ looks better from a user point of view. Anyone else has an opinion?
> >
> > Regards,
> > Olivier
> 
> Regards,
> Helin