On Thu, Mar 24, 2022 at 7:27 AM Templin (US), Fred L <fred.l.temp...@boeing.com> wrote: > > Tom - see below: > > > -----Original Message----- > > From: Tom Herbert [mailto:t...@herbertland.com] > > Sent: Thursday, March 24, 2022 6:22 AM > > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > > Cc: Eggert, Lars <l...@netapp.com>; int-area <int-area@ietf.org>; > > l...@eggert.org > > Subject: Re: [Int-area] IP Parcels improves performance for end systems > > > > On Wed, Mar 23, 2022 at 10:47 AM Templin (US), Fred L > > <fred.l.temp...@boeing.com> wrote: > > > > > > Tom, looks like you have switched over to HTML which can be a real > > > conversation-killer. > > > > > > But, to some points you raised that require a response: > > > > > > >You can't turn it off UDP checksums for IPv6 (except for narrow case of > > > >encapsulation). > > > > > > > > > > > > That sounds like a good reason to continue to use IPv4 – at least as far > > > as end system > > > > > > addressing is concerned – right? > > > > > > Not at all. All NICs today provide checksum offload and so it's > > basically zero cost to perform the UDP checksum. The fact that we > > don't have to do extra checks on the UDPv6 checksum field to see if > > it's zero actually is a performance improvement over UDPv4. (btw, I > > will present implementation of the Internet checksum at TSVGWG Friday, > > this will include discussion of checksum offloads). > > Actually, my assertion wasn't good to begin with because for IPv6 even if UDP > checksums are turned off the OMNI encapsulation layer includes a checksum > that ensures the integrity of the IPv6 header. UDP checksums off for IPv6 when > OMNI encapsulation is used is perfectly fine. > I assume you are referring to RFC6935 and RFC6936 that allow the UDPv6 to be zero for tunneling with a very constrained set of conditions.
> > > >If it's a standard per packet Internet checksum then a lot of HW could > > > >do it. If it's something like CRC32 then probably not. > > > > > > > > > > > > The integrity check is covered in RFC5327, and I honestly haven’t had a > > > chance to > > > > > > look at that myself yet. > > > > > > > > > > > > >LTP is a nice experiment, but I'm more interested as to the interaction > > > >between IP parcels and TCP or QUIC. > > > > > > > > > > > > Please be aware that while LTP may seem obscure at the moment that may be > > > changing now > > > > > > that the core DTN standards have been published. As DTN use becomes more > > > widespread I > > > > > > think we can see LTP also come into wider adoption. > > > > > > My assumption is that IP parcels is intended to be a general solution > > of all protocols. Maybe in the next draft you could discuss the > > details of TCP in IP parcels including how to offload the TCP > > checksum. > > I could certainly add that. For TCP, each of the concatenated segments would > include its own TCP header with checksum field included. Any hardware that > knows the structure of an IP Parcel can then simply do the TCP checksum > offload function for each segment. To be honest, the odds of ever getting support in NIC hardware for IP parcels are extremely slim. Hardware vendors are driven by economics, so the only way they would do that would be to demonstrate widespread deployment of the protocol. But even then, with all the legacy hardware in deployment it will take many years before there's any appreciable traction. IMO, the better approach is to figure out how to leverage the existing hardware features for use with IP parcels. > > > > >There was quite a bit of work and discussion on this in Linux. I believe > > > >the deviation from the standard was motivated by some > > > > > > >deployed devices required the IPID be set on receive, and setting IPID > > > >with DF equals to 1 is thought to be innocuous. You may > > > > > > >want to look at Alex Duyck's papers on UDP GSO, he wrote a lot of code > > > >in this area. > > > > > > > > > > > > RFC6864 has quite a bit to say about coding IP ID with DF=1 – mostly in > > > the negative. > > > > > > But, what I have seen in the linux code seems to indicate that there is > > > not even any > > > > > > coordination between the GSO source and the GRO destination – instead, > > > GRO simply > > > > > > starts gluing together packets that appear to have consecutive IP IDs > > > without ever first > > > > > > checking that they were sent by a peer that was earnestly doing GSO. > > > These aspects > > > > > > would make it very difficult to work GSO/GRO into an IETF standard, plus > > > it doesn’t > > > > > > work for IPv6 at all where there is no IP ID included by default. IP > > > Parcels addresses > > > > > > all of these points, and can be made into a standard. > > > > > > Huh? GRO/GSO works perfectly fine with IPV6. > > Where is the spec for that? My understanding is that GSO/GRO leverages the > IP ID for IPv4. But, for IPv6, there is no IP ID unless you include a > Fragment Header. > Does IPv6 somehow do GSO/GRO differently? > GRO and GSO don't use the IPID to match a flow. The primary match is the TCP 4-tuple. There's also another possibility with IPv6-- use jumbograms. For instance, instead of GRO reassembling segments up to a 64K packet, it could be modified to reassemble up to a 4G packet using IPv6 jumbograms where one really big packet is given to the stack. But we probably don't even need jumbograms for that. In Linux, GRO might be taught to reassemble up to 4G super packet and set a flag bit in the skbuf to ignore the IP payload field and get the length from the skbuf len field (as though a jumbogram was received). This trick would work for IPV4 and IPv6 and GSO as well. It should also work TSO if the device takes the IP payload length to be that for each segment. Tom > Thanks - Fred > > > Tom > > > > > > > > > > > Fred > > > > > > > > > > > > From: Tom Herbert [mailto:t...@herbertland.com] > > > Sent: Wednesday, March 23, 2022 9:37 AM > > > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > > > Cc: Eggert, Lars <l...@netapp.com>; int-area <int-area@ietf.org>; > > > l...@eggert.org > > > Subject: Re: [EXTERNAL] Re: [Int-area] IP Parcels improves performance > > > for end systems > > > > > > > > > > > > EXT email: be mindful of links/attachments. > > > > > > > > > > > > > > > > > > > > > On Wed, Mar 23, 2022, 9:54 AM Templin (US), Fred L > > > <fred.l.temp...@boeing.com> wrote: > > > > > > Hi Tom, > > > > > > > -----Original Message----- > > > > From: Tom Herbert [mailto:t...@herbertland.com] > > > > Sent: Wednesday, March 23, 2022 6:19 AM > > > > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > > > > Cc: Eggert, Lars <l...@netapp.com>; int-area@ietf.org; l...@eggert.org > > > > Subject: Re: [Int-area] IP Parcels improves performance for end systems > > > > > > > > On Tue, Mar 22, 2022 at 10:38 AM Templin (US), Fred L > > > > <fred.l.temp...@boeing.com> wrote: > > > > > > > > > > Tom, see below: > > > > > > > > > > > -----Original Message----- > > > > > > From: Tom Herbert [mailto:t...@herbertland.com] > > > > > > Sent: Tuesday, March 22, 2022 10:00 AM > > > > > > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > > > > > > Cc: Eggert, Lars <l...@netapp.com>; int-area@ietf.org > > > > > > Subject: Re: [Int-area] IP Parcels improves performance for end > > > > > > systems > > > > > > > > > > > > On Tue, Mar 22, 2022 at 7:42 AM Templin (US), Fred L > > > > > > <fred.l.temp...@boeing.com> wrote: > > > > > > > > > > > > > > Lars, I did a poor job of answering your question. One of the > > > > > > > most important aspects of > > > > > > > > > > > > > > IP Parcels in relation to TSO and GSO/GRO is that transports get > > > > > > > to use a full 4MB buffer > > > > > > > > > > > > > > instead of the 64KB limit in current practices. This is possible > > > > > > > due to the IP Parcel jumbo > > > > > > > > > > > > > > payload option encapsulation which provides a 32-bit length field > > > > > > > instead of just a 16-bit. > > > > > > > > > > > > > > By allowing the transport to present the IP layer with a buffer > > > > > > > of up to 4MB, it reduces > > > > > > > > > > > > > > the overhead, minimizes system calls and interrupts, etc. > > > > > > > > > > > > > > > > > > > > > > > > > > > > So, yes, IP Parcels is very much about improving the performance > > > > > > > for end systems in > > > > > > > > > > > > > > comparison with current practice (GSO/GRO and TSO). > > > > > > > > > > > > Hi Fred, > > > > > > > > > > > > The nice thing about TSO/GSO/GRO is that they don't require any > > > > > > changes to the protocol as just implementation techniques, also > > > > > > they're one sided opitmizations meaning for instance that TSO can be > > > > > > used at the sender without requiring GRO to be used at the receiver. > > > > > > My understanding is that IP parcels requires new protocol that would > > > > > > need to be implemented on both endpoints and possibly in some > > > > > > routers. > > > > > > > > > > It is not entirely true that the protocol needs to be implemented on > > > > > both > > > > > endpoints . Sources that send IP Parcels send them into a > > > > > Parcel-capable path > > > > > which ends at either the final destination or a router for which the > > > > > next hop is > > > > > not Parcel-capable. If the Parcel-capable path extends all the way to > > > > > the final > > > > > destination, then the Parcel is delivered to the destination which > > > > > knows how > > > > > to deal with it. If the Parcel-capable path ends at a router > > > > > somewhere in the > > > > > middle, the router opens the Parcel and sends each enclosed segment > > > > > as an > > > > > independent IP packet. The final destination is then free to apply > > > > > GRO to the > > > > > incoming IP packets even if it does not understand Parcels. > > > > > > > > > > IP Parcels is about efficient shipping and handling just like the > > > > > major online > > > > > retailer service model I described during the talk. The goal is to > > > > > deliver the > > > > > fewest and largest possible parcels to the final destination rather > > > > > than > > > > > delivering lots of small IP packets. It is good for the network and > > > > > good for > > > > > the end systems both. If this were not true, then Amazon would send > > > > > the > > > > > consumer 50 small boxes with 1 item each instead of 1 larger box with > > > > > all > > > > > 50 items inside. And, we all know what they would choose to do. > > > > > > > > > > > Do you have data that shows the benefits of IP Parcels in light of > > > > > > these requirements? > > > > > > > > > > I have data that shows that GSO/GRO is good for packaging sizes up to > > > > > 64KB > > > > > even if the enclosed segments will require IP fragmentation upon > > > > > transmission. > > > > > The data implies that even larger packaging sizes (up to a maximum of > > > > > 4MB) > > > > > would be better still. > > > > > > > > > > > > > Fred, > > > > > > > > You seem to be only looking at the problem from a per packet cost > > > > point of view. There is also per byte cost, particularly in the > > > > computation of the TCP/UDP checksum. The cost is hidden in modern > > > > implementations by checksum offload, and for segmentation offload we > > > > have methods to preserve the utility of checksum offload. IP parcels > > > > will have to also leverage checksum offload, because if the checksum > > > > is not offloaded then the cost of computing the payload checksum in > > > > CPU would dwarf any benefits we'd get by using segments larger than > > > > 64K. > > > > > > There is plenty of opportunity to apply hardware checksum offload since > > > the structure of a Parcel will be very standard. My experiments have been > > > with a protocol called LTP which is layered over UDP/IP as some other > > > upper layer protocols are. LTP includes a segment-by-segment checksum > > > that is used at its level in the absence of lower layer integrity checks, > > > so > > > for larger Parcels LTP would use that and turn off UDP checksums > > > altogether. > > > > > > > > > > > > You can't turn it off UDP checksums for IPv6 (except for narrow case of > > > encapsulation). > > > > > > > > > > > > As far as I am aware, there are currently no hardware > > > checksum offload implementations available for calculating the > > > LTP checksums. > > > > > > > > > > > > If it's a standard per packet Internet checksum then a lot of HW could do > > > it. If it's something like CRC32 then probably not. > > > > > > > > > > > > LTP is a nice experiment, but I'm more interested as to the interaction > > > between IP parcels and TCP or QUIC. > > > > > > > > > > > > > > > Speaking of standard, AFAICT GSO/GRO are doing something very > > > non-standard. GSO seems to be coding the IP ID field in the IPv4 > > > headers of packets with DF=1 which goes against RFC 6864. When > > > DF=1, GSO cannot simply claim the IP ID and code it as if there were > > > some sort of protocol. Or, if it does, there would be no way to > > > standardize it. > > > > > > > > > > > > There was quite a bit of work and discussion on this in Linux. I believe > > > the deviation from the standard was motivated by some deployed > > devices required the IPID be set on receive, and setting IPID with DF > > equals to 1 is thought to be innocuous. You may want to look at Alex > > Duyck's papers on UDP GSO, he wrote a lot of code in this area. > > > > > > > > > > > > Tom > > > > > > > > > > > > > > > Fred > > > > > > > > > > > Tom > > > > > > > > > Fred > > > > > > > > > > > Thanks, > > > > > > Tom > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks - Fred > > > > > > > > > > > > > > _______________________________________________ > > > > > > > Int-area mailing list > > > > > > > Int-area@ietf.org > > > > > > > https://www.ietf.org/mailman/listinfo/int-area > _______________________________________________ Int-area mailing list Int-area@ietf.org https://www.ietf.org/mailman/listinfo/int-area
