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

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

> -----Original Message-----
> From: Liu, Jijiang
> Sent: Thursday, December 04, 2014 2:08 AM
> To: Olivier MATZ
> Cc: Ananyev, Konstantin; dev@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH v5 2/3] mbuf:add three TX ol_flags and repalce PKT_TX_VXLAN_CKSUM
> 
> Hi Olivier,
> 
> 
> > -----Original Message-----
> > From: Olivier MATZ [mailto:olivier.matz@6wind.com]
> > Sent: Wednesday, December 3, 2014 10:42 PM
> > To: Ananyev, Konstantin; Liu, Jijiang; dev@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 */
> >
> > with PKT_TX_IP_CKSUM implies PKT_TX_IPV4
> >
> >
> > Solution 2/ looks better from a user point of view. Anyone else has an opinion?
> 
> Let's think about these IPv4/6 flags in terms of checksum and IP version/type,
> 
> 1. For IPv6
> IP checksum is meaningful only for IPv4,  so we define 'PKT_TX_IPV6      /* packet is IPv6 */' to tell driver/HW that this is IPV6 packet,
> here we don't talk about the checksum for IPv6 as it is meaningless. Right?
> 
> PKT_TX_IPV6      /* packet is IPv6 */         ------ IP type: v6;  HW checksum: meaningless
> 
> 2. For IPv4,
> My patch:
> 
> PKT_TX_IP_CKSUM  /* packet is IPv4, and we want hw cksum */--------------------------IP type: v4;  HW checksum: Yes
> PKT_TX_IPV4      /* packet is IPv4, and we don't want hw cksum */ ----------------------- IP type: v4;  HW checksum: No
> 
> You want:
> PKT_TX_IP_CKSUM  /* we want hw IP cksum */-------------------------- IP type: v4;  HW checksum: Yes
> PKT_TX_IPV4      /* packet is IPv4*/ ------------------------  IP type: v4; HW checksum: yes or no?
>                                                                                                        driver/HW don't know, just know this is packet with IPv4 header.
>                                                                                                        HW checksum: meaningless??

Yep, that's why I also don't like that suggestion: PKT_TX_IPV4 itself doesn't contain all information.
PMD will have to check PKT_TX_IP_CKSUM  anyway.
Konstantin

> 
> > Regards,
> > Olivier