On Fri, Dec 4, 2020 at 3:20 AM Edward Cree <ecree.xil...@gmail.com> wrote: > > On 03/12/2020 19:52, John Ousterhout wrote: > > Homa uses GRO to collect batches of packets for protocol processing, > > but there are times when it wants to push a batch of packet up through > > the stack immediately (it doesn't want any more packets to be > > processed at NAPI level before pushing the batch up). However, I can't > > see a way to achieve this goal. > It's kinda hacky, but you might be able to call netif_receive_skb_internal() > yourself, and then return ERR_PTR(-EINPROGRESS), so that dev_gro_receive() > returns GRO_CONSUMED. > Of course, you'd need to be careful about out-of-order issues in case > any earlier homa packets were still sitting in the rx_list.
It doesn't appear to me that this approach will work, because the packet I want to force up through the stack is not the new one being passed into homa_gro_receive, but one of the packets on the list passed in as the first argument (gro_head in dev_gro_receive). Removing a packet from this list looks tricky, because it also requires updating a count in the napi structure, which homa_gro_receive doesn't have immediate access to. I might be able to figure out a way to get the napi pointer, but this is starting to feel pretty hacky (and brittle w.r.t. kernel changes). BTW, out-of-order issues don't matter for Homa; this is one of the areas where the "protocol independent" parts of the networking code build in TCP-specific assumptions, which are either unnecessary or, in some cases, problematic for Homa. Thanks anyway for the suggestion. -John-
