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Commit 9c4c3252 authored by Flavio Leitner's avatar Flavio Leitner Committed by David S. Miller
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skbuff: preserve sock reference when scrubbing the skb. 



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: default avatarFlavio Leitner <fbl@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f5646501

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);