Hi Thomas, > -----Original Message----- > From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com] > Sent: Thursday, December 04, 2014 10:45 AM > To: Ananyev, Konstantin; Olivier MATZ > Cc: dev at dpdk.org; Liu, Jijiang > Subject: Re: [dpdk-dev] [PATCH v5 2/3] mbuf:add three TX ol_flags and repalce > PKT_TX_VXLAN_CKSUM > > Hi, > > 2014-12-04 10:23, Ananyev, Konstantin: > > From: Liu, Jijiang > > > From: Olivier MATZ [mailto:olivier.matz at 6wind.com] > > > > 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. > > I prefer solution 2 because a flag should bring only 1 information.
Why is that? For example in mbuf we already have a flag that brings 2 things: PKT_TX_IP_CKSUM /* packet is IPv4, and we want hw cksum */ If it would be possible to compress 10 meanings into 1 bit, I would happily do that. Unfortunately, it is rarely possible :) > It's simply saner and could fit to more situations in the future. Could you give an example of such situation? I personally couldn't come up with the case where #2 would have any real advantage. Konstantin > > -- > Thomas
