On 06/25/2018 09:15 PM, Cong Wang wrote: > On Mon, Jun 25, 2018 at 8:59 AM Flavio Leitner <fbl@xxxxxxxxxx> wrote: >> >> The sock reference is lost when scrubbing the packet and that breaks >> TSQ (TCP Small Queues) and XPS (Transmit Packet Steering) causing >> performance impacts of about 50% in a single TCP stream when crossing >> network namespaces. >> >> XPS breaks because the queue mapping stored in the socket is not >> available, so another random queue might be selected when the stack >> needs to transmit something like a TCP ACK, or TCP Retransmissions. >> That causes packet re-ordering and/or performance issues. >> >> TSQ breaks because it orphans the packet while it is still in the >> host, so packets are queued contributing to the buffer bloat problem. > > Why should TSQ in one stack care about buffer bloat in another stack? > > Actually, I think the current behavior is correct, once the packet leaves > its current stack (or netns), it should relief the backpressure on TCP > socket in this stack, whether it will be queued in another stack is beyond > its concern. This breaks the isolation between networking stacks. > We discussed about this during netconf Cong, nobody was against this planned removal. When a packet is attached to a socket, we should keep the association as much as possible. Only when a new association needs to be done, skb_orphan() needs to be called. Doing this skb_orphan() too soon breaks back pressure in general, this is bad, since a socket can evades SO_SNDBUF limits. I am not sure why the patch is so complex, I would have simply removed the skb_orphan(). -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
