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

["Liu, Jijiang" <jijiang.liu@intel.com>]

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??

> Regards,
> Olivier