Jesper Dangaard Brouer <brouer@xxxxxxxxxx> writes: > On Tue, 25 Jun 2019 03:19:22 +0000 > "Machulsky, Zorik" <zorik@xxxxxxxxxx> wrote: > >> On 6/23/19, 7:21 AM, "Jesper Dangaard Brouer" <brouer@xxxxxxxxxx> wrote: >> >> On Sun, 23 Jun 2019 10:06:49 +0300 <sameehj@xxxxxxxxxx> wrote: >> >> > This commit implements the basic functionality of drop/pass logic in the >> > ena driver. >> >> Usually we require a driver to implement all the XDP return codes, >> before we accept it. But as Daniel and I discussed with Zorik during >> NetConf[1], we are going to make an exception and accept the driver >> if you also implement XDP_TX. >> >> As we trust that Zorik/Amazon will follow and implement XDP_REDIRECT >> later, given he/you wants AF_XDP support which requires XDP_REDIRECT. >> >> Jesper, thanks for your comments and very helpful discussion during >> NetConf! That's the plan, as we agreed. From our side I would like to >> reiterate again the importance of multi-buffer support by xdp frame. >> We would really prefer not to see our MTU shrinking because of xdp >> support. > > Okay we really need to make a serious attempt to find a way to support > multi-buffer packets with XDP. With the important criteria of not > hurting performance of the single-buffer per packet design. > > I've created a design document[2], that I will update based on our > discussions: [2] https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp-multi-buffer01-design.org > > The use-case that really convinced me was Eric's packet header-split. > > > Lets refresh: Why XDP don't have multi-buffer support: > > XDP is designed for maximum performance, which is why certain driver-level > use-cases were not supported, like multi-buffer packets (like jumbo-frames). > As it e.g. complicated the driver RX-loop and memory model handling. > > The single buffer per packet design, is also tied into eBPF Direct-Access > (DA) to packet data, which can only be allowed if the packet memory is in > contiguous memory. This DA feature is essential for XDP performance. > > > One way forward is to define that XDP only get access to the first > packet buffer, and it cannot see subsequent buffers. For XDP_TX and > XDP_REDIRECT to work then XDP still need to carry pointers (plus > len+offset) to the other buffers, which is 16 bytes per extra buffer. Yeah, I think this would be reasonable. As long as we can have a metadata field with the full length + still give XDP programs the ability to truncate the packet (i.e., discard the subsequent pages) I think many (most?) use cases will work fine without having access to the full packet data... -Toke
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