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From: "Eelco Chaudron" <echaudro@redhat.com>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: "Jesper Dangaard Brouer" <brouer@redhat.com>,
	"Machulsky, Zorik" <zorik@amazon.com>,
	"Jubran, Samih" <sameehj@amazon.com>,
	davem@davemloft.net, 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
Subject: Re: XDP multi-buffer incl. jumbo-frames (Was: [RFC V1 net-next 1/1] net: ena: implement XDP drop support)
Date: Fri, 28 Jun 2019 13:49:43 +0200
Message-ID: <5127F708-7CDD-4471-9767-D8C87DC23888@redhat.com> (raw)
In-Reply-To: <87y31m884a.fsf@toke.dk>



On 28 Jun 2019, at 9:46, Toke Høiland-Jørgensen wrote:

> "Eelco Chaudron" <echaudro@redhat.com> writes:
>
>> On 26 Jun 2019, at 10:38, Jesper Dangaard Brouer wrote:
>>
>>> 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.
>>
>>
>> I’ve seen various network processor HW designs, and they normally 
>> get
>> the first x bytes (128 - 512) which they can manipulate
>> (append/prepend/insert/modify/delete).
>>
>> There are designs where they can “page in” the additional 
>> fragments
>> but it’s expensive as it requires additional memory transfers. But 
>> the
>> majority do not care (cannot change) the remaining fragments. Can 
>> also
>> not think of a reason why you might want to remove something at the 
>> end
>> of the frame (thinking about routing/forwarding needs here).
>>
>> If we do want XDP to access other fragments we could do this through 
>> a
>> helper which swaps the packet context?
>
> Yeah, I was also going to suggest a helper for that. It doesn't
> necessarily need to swap the packet context, it could just return a 
> new
> pointer?

Yes that will work, my head was still thinking ASICs where there is 
limited SRAM space…

  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
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 [this message]
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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