Re: [dpdk-dev] [PATCH v2 1/4] ethdev: add Rx offload outer UDP checksum definition

[Thomas Monjalon <thomas@monjalon.net>]

08/10/2018 14:25, Jerin Jacob:
> From: Ferruh Yigit <ferruh.yigit@intel.com>
> > On 10/8/2018 12:55 PM, Jerin Jacob wrote:
> > > From: Ferruh Yigit <ferruh.yigit@intel.com>
> > >> On 10/8/2018 10:37 AM, Jerin Jacob wrote:
> > >>> From: Thomas Monjalon <thomas@monjalon.net>
> > >>>> 08/10/2018 10:24, Jerin Jacob:
> > >>>>> From: Ferruh Yigit <ferruh.yigit@intel.com>
> > >>>>>> On 10/6/2018 1:18 PM, Ananyev, Konstantin wrote:
> > >>>>>>> From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com]
> > >>>>>>>> From: Thomas Monjalon <thomas@monjalon.net>
> > >>>>>>>>> However, we should re-visit the flag PKT_RX_EIP_CKSUM_BAD.
> > >>>>>>>>
> > >>>>>>>> Do we need to block this patch due to the exiting PKT_RX_EIP_CKSUM_BAD
> > >>>>>>>> definition?
> > >>>>>>>>
> > >>>>>>>> I already added the author of the PKT_RX_EIP_CKSUM_BAD flag and ethdev and mbuf
> > >>>>>>>> maintainers in this list. So what else I need make forward progress
> > >>>>>>>> on this patch?
> > >>>>>>>>
> > >>>>>>>> I think, the definition of PKT_RX_EIP_CKSUM_BAD based on HW capability. It
> > >>>>>>>> is safe to assume that ALL HW can support CKSUM BAD if the feature is
> > >>>>>>>> available and hence it is more portable.
> > >>>>>>>
> > >>>>>>> Yes, as I remember PKT_RX_EIP_CKSUM_BAD is based on DEV_RX_OFFLOAD_OUTER_IPV4_CKSUM.
> > >>>>>>
> > >>>>>> Switching to two bit won't reduce the portability, HW supports only reporting
> > >>>>>> CKSUM_BAD can set BAD || UNKNOWN.
> > >>>>>
> > >>>>> UNKNOWN is not a bit. It is represented as 0. It spec has 2 bit, then
> > >>>>> driver need to report GOOD as well.
> > >>>>>
> > >>>>> Same applies for PKT_RX_EL4_CKSUM as well.
> > >>>>>
> > >>>>>>
> > >>>>>> And I think patch is not blocked by PKT_RX_EIP_CKSUM_BAD, it can be changed
> > >>>>>> separately, for this patch question is can we represent PKT_RX_EL4_CKSUM_* with
> > >>>>>> two bits, to have BAD/GOOD/UNKNOWN?
> > >>>>
> > >>>> Yes, exact.
> > >>>>
> > >>>> PKT_RX_EIP_CKSUM_BAD must be left aside.
> > >>>> We should just avoid taking it as a reference.
> > >>>> And we can reconsider its definition later.
> > >>>
> > >>> OK.
> > >>>
> > >>> IMO, Using 2 bit scheme for tunneled checksum has following performance
> > >>> issue from driver side.
> > >>>
> > >>> Driver need to mark the packet as GOOD. All the HW can support
> > >>> detection of BAD. That not necessary mean GOOD in case of tunnel packet,
> > >>> so driver has to detect the packet is tunneled and packet is not BAD
> > >>> then mark GOOD.
> > >>
> > >> Yes UNKNOWN is not a bit, but a state, why don't use it? Why driver has to check
> > >> it is GOOD?
> > >
> > > The application is going to check is it GOOD or not. Not the driver,
> > > Right? My concern was, If application starts dropping the packet instead checking the BAD, if
> > > it checks == !GOOD.
> > 
> > Got it, but when 2 bits state introduced, app should check if check == BAD for
> > drop decision, because it is not GOOD || BAD anymore.
> 
> Got it.
> 
> > 
> > >
> > >>
> > >> 0x0 => UNKNOWN
> > >> 0x1 => BAD
> > >> 0x2 => GOOD
> > >> 0x3 => ? (invalid perhaps)
> > >>
> > >> HW that supports detecting good packets can set BAD || GOOD state, HW can detect
> > >> only BAD packet can set BAD || UNKNOWN state.
> > >>
> > >> If BAD is not set, there is an ambiguity of state, lets clarify it in lower
> > >> level, if it is UNKNOWN, let application know it is UNKNOWN.
> > >
> > > OK.
> > >
> > > How about the following then?
> > >
> > > /**
> > >  * Mask of bits used to determine the status of outer RX L4 checksum.
> > >  * - PKT_RX_EL4_CKSUM_UNKNOWN: no information about the outer RX L4 checksum
> > >  * - PKT_RX_EL4_CKSUM_BAD: the outer L4 checksum in the packet is wrong
> > >  * - PKT_RX_EL4_CKSUM_GOOD: the outer L4 checksum in the packet is valid
> > >  * - PKT_RX_EL4_CKSUM_INVALID: invalid outer L4 checksum state.
> > >  *
> > >  * The detection of PKT_RX_EL4_CKSUM_GOOD shall be based on the given
> > >  * HW capability, At minimum, the PMD should support
> > >  * PKT_RX_EL4_CKSUM_UNKNOWN  and PKT_RX_EL4_CKSUM_BAD states
> > >  * if the offload is available.
> > >  */
> > > #define PKT_RX_EL4_CKSUM_MASK   ((1ULL << 21) | (1ULL << 22))
> > >
> > > #define PKT_RX_IP_CKSUM_UNKNOWN 0
> > > #define PKT_RX_IP_CKSUM_BAD     (1ULL << 21)
> > > #define PKT_RX_IP_CKSUM_GOOD    (1ULL << 22)
> > > #define PKT_RX_IP_CKSUM_INVALID ((1ULL << 21) | (1ULL << 22))
> > 
> > Looks good to me.
> 
> If there is no objection with above flag definition, I will send the v3 with that.

Just one objection about the name.
Why naming it EL4 and commenting as outer L4?
I think we should choose between "external" and "outer".
Convention seems to be choosing "outer" word.
So I suggest PKT_RX_OUTER_L4_CKSUM_*.