From: Jesper Dangaard Brouer <brouer@redhat.com> To: "Toke Høiland-Jørgensen" <toke@redhat.com> Cc: "Machulsky\, Zorik" <zorik@amazon.com>, "Jubran\, Samih" <sameehj@amazon.com>, "davem\@davemloft.net" <davem@davemloft.net>, "netdev\@vger.kernel.org" <netdev@vger.kernel.org>, "Woodhouse\, David" <dwmw@amazon.co.uk>, "Matushevsky\, Alexander" <matua@amazon.com>, "Bshara\, Saeed" <saeedb@amazon.com>, "Wilson\, Matt" <msw@amazon.com>, "Liguori\, Anthony" <aliguori@amazon.com>, "Bshara\, Nafea" <nafea@amazon.com>, "Tzalik\, Guy" <gtzalik@amazon.com>, "Belgazal\, Netanel" <netanel@amazon.com>, "Saidi\, Ali" <alisaidi@amazon.com>, "Herrenschmidt\, Benjamin" <benh@amazon.com>, "Kiyanovski\, Arthur" <akiyano@amazon.com>, Daniel Borkmann <borkmann@iogearbox.net>, Ilias Apalodimas <ilias.apalodimas@linaro.org>, Alexei Starovoitov <alexei.starovoitov@gmail.com>, Jakub Kicinski <jakub.kicinski@netronome.com>, "xdp-newbies\@vger.kernel.org" <xdp-newbies@vger.kernel.org>, brouer@redhat.com Subject: Re: XDP multi-buffer incl. jumbo-frames (Was: [RFC V1 net-next 1/1] net: ena: implement XDP drop support) Date: Wed, 26 Jun 2019 16:40:59 +0200 Message-ID: <20190626164059.4a9511cf@carbon> (raw) In-Reply-To: <87a7e4d0nj.fsf@toke.dk> On Wed, 26 Jun 2019 13:52:16 +0200 Toke Høiland-Jørgensen <toke@redhat.com> wrote: > Jesper Dangaard Brouer <brouer@redhat.com> writes: > > > On Tue, 25 Jun 2019 03:19:22 +0000 > > "Machulsky, Zorik" <zorik@amazon.com> wrote: > > > >> On 6/23/19, 7:21 AM, "Jesper Dangaard Brouer" <brouer@redhat.com> wrote: > >> > >> On Sun, 23 Jun 2019 10:06:49 +0300 <sameehj@amazon.com> 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) You touch upon some interesting complications already: 1. It is valuable for XDP bpf_prog to know "full" length? (if so, then we need to extend xdp ctx with info) But if we need to know the full length, when the first-buffer is processed. Then realize that this affect the drivers RX-loop, because then we need to "collect" all the buffers before we can know the length (although some HW provide this in first descriptor). We likely have to change drivers RX-loop anyhow, as XDP_TX and XDP_REDIRECT will also need to "collect" all buffers before the packet can be forwarded. (Although this could potentially happen later in driver loop when it meet/find the End-Of-Packet descriptor bit). 2. Can we even allow helper bpf_xdp_adjust_tail() ? Wouldn't it be easier to disallow a BPF-prog with this helper, when driver have configured multi-buffer? Or will it be too restrictive, if jumbo-frame is very uncommon and only enabled because switch infra could not be changed (like Amazon case). Perhaps it is better to let bpf_xdp_adjust_tail() fail runtime? > I think many (most?) use cases will work fine without having access > to the full packet data... I agree. Other people should voice their concerns if they don't agree... -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
next prev parent reply index Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-06-23 7:06 [RFC V1 net-next 0/1] Introduce xdp to ena sameehj 2019-06-23 7:06 ` [RFC V1 net-next 1/1] net: ena: implement XDP drop support sameehj 2019-06-23 14:09 ` Jesper Dangaard Brouer 2019-06-23 14:21 ` Jesper Dangaard Brouer 2019-06-25 3:19 ` Machulsky, Zorik 2019-06-26 8:38 ` XDP multi-buffer incl. jumbo-frames (Was: [RFC V1 net-next 1/1] net: ena: implement XDP drop support) Jesper Dangaard Brouer 2019-06-26 11:52 ` Toke Høiland-Jørgensen 2019-06-26 14:40 ` Jesper Dangaard Brouer [this message] 2019-06-26 15:01 ` Toke Høiland-Jørgensen 2019-06-26 15:20 ` Willem de Bruijn 2019-06-26 16:42 ` Jonathan Lemon 2019-06-26 20:00 ` Jesper Dangaard Brouer 2019-06-27 22:07 ` Jonathan Lemon 2019-06-28 8:46 ` Jesper Dangaard Brouer 2019-06-26 15:14 ` Toke Høiland-Jørgensen 2019-06-26 16:36 ` Jesper Dangaard Brouer 2019-06-28 7:14 ` Eelco Chaudron 2019-06-28 7:46 ` Toke Høiland-Jørgensen 2019-06-28 11:49 ` Eelco Chaudron 2019-06-28 8:22 ` Jesper Dangaard Brouer 2019-06-23 14:28 ` [RFC V1 net-next 1/1] net: ena: implement XDP drop support David Ahern 2019-06-23 14:51 ` Maciej Fijalkowski
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