On 26 Jun 2019, at 10:38, Jesper Dangaard Brouer wrote:
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 driverif 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 ourdiscussions: [2] https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp-multi-buffer01-design.orgThe 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 incontiguous 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?
//Eelco
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