On Sun, 09 Apr 2017 19:14:06 -0700 (PDT) David Miller <davem@xxxxxxxxxxxxx> wrote: > From: Florian Fainelli <f.fainelli@xxxxxxxxx> > Date: Sun, 9 Apr 2017 19:05:39 -0700 > > > In order for a NIC and its driver to support XDP, it sounds like we need: > > > > - page-based RX > > Not exactly. The requirement is actually that the packet-page is _writable_. These packet-pages come from the NIC DMA engine, and this complicates keeping them writable, in the case where a RX-page is used for containing two (or more) packets. Careful use of the DMA API does make it possible to page packet sharing to co-exist with XDP (consult Alex Duyck to review such driver changes). > > - TX multiqueue support > > Also, not really required. > > What you need to be able to do is to provide enough space in each > RX buffer for: > > 1) a full size frame > 2) 256 bytes (XDP_PACKET_HEADROOM) of headroom > > This is XDP's main set of requirements, a linear buffer and enough > room to push XDP_PACKET_HEADROOM's worth of headers. True. > Then if you want to be able to easily wrap the RX packet into an SKB > for XDP_PASS, you need to have enough tailroom for skb_shared_info() > which you basically give to something like build_skb(). True this is a stack requirement. > If you look at __build_skb() it's comment states "Caller provides > space holding head and skb_shared_info". > > For XDP_TX you just have to be able to queue up a raw skb'less packet > into your transmit queue. TX multiqueue is not required for this to > work. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
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