skbuff: preserve sock reference when scrubbing the skb. (9c4c3252) · Commits · 戴 / test

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. Preserving the sock reference fixes both issues. The socket is orphaned anyways in the receiving path before any relevant action and on TX side the netfilter checks if the reference is local before use it. Signed-off-by:

Flavio Leitner <fbl@redhat.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

+5 −5

Original line number	Diff line number	Diff line
		@@ -733,11 +733,11 @@ tcp_limit_output_bytes - INTEGER
		Controls TCP Small Queue limit per tcp socket.
		TCP bulk sender tends to increase packets in flight until it
		gets losses notifications. With SNDBUF autotuning, this can
		result in a large amount of packets queued in qdisc/device
		on the local machine, hurting latency of other flows, for
		typical pfifo_fast qdiscs.
		tcp_limit_output_bytes limits the number of bytes on qdisc
		or device to reduce artificial RTT/cwnd and reduce bufferbloat.
		result in a large amount of packets queued on the local machine
		(e.g.: qdiscs, CPU backlog, or device) hurting latency of other
		flows, for typical pfifo_fast qdiscs. tcp_limit_output_bytes
		limits the number of bytes on qdisc or device to reduce artificial
		RTT/cwnd and reduce bufferbloat.
		Default: 262144

		tcp_challenge_ack_limit - INTEGER

net/core/skbuff.c

+0 −1

Original line number	Diff line number	Diff line
		@@ -4911,7 +4911,6 @@ void skb_scrub_packet(struct sk_buff *skb, bool xnet)
		return;

		ipvs_reset(skb);
		skb_orphan(skb);
		skb->mark = 0;
		}
		EXPORT_SYMBOL_GPL(skb_scrub_packet);

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