From f2f872f9272a79a1048877ea14c15576f46c225e Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 30 Jul 2013 17:55:08 -0700 Subject: [PATCH] netem: Introduce skb_orphan_partial() helper Commit 547669d483e578 ("tcp: xps: fix reordering issues") added unexpected reorders in case netem is used in a MQ setup for high performance test bed. ETH=eth0 tc qd del dev $ETH root 2>/dev/null tc qd add dev $ETH root handle 1: mq for i in `seq 1 32` do tc qd add dev $ETH parent 1:$i netem delay 100ms done As all tcp packets are orphaned by netem, TCP stack believes it can set skb->ooo_okay on all packets. In order to allow producers to send more packets, we want to keep sk_wmem_alloc from reaching sk_sndbuf limit. We can do that by accounting one byte per skb in netem queues, so that TCP stack is not fooled too much. Tested: With above MQ/netem setup, scaling number of concurrent flows gives linear results and no reorders/retransmits lpq83:~# for n in 1 10 20 30 40 50 60 70 80 90 100 do echo -n "n:$n " ; ./super_netperf $n -H 10.7.7.84; done n:1 198.46 n:10 2002.69 n:20 4000.98 n:30 6006.35 n:40 8020.93 n:50 10032.3 n:60 12081.9 n:70 13971.3 n:80 16009.7 n:90 17117.3 n:100 17425.5 Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/net/sock.h | 1 + net/core/sock.c | 19 +++++++++++++++++++ net/sched/sch_netem.c | 5 +---- 3 files changed, 21 insertions(+), 4 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index b9f2b095b1ab..53d4714709a1 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1520,6 +1520,7 @@ extern struct sk_buff *sock_rmalloc(struct sock *sk, unsigned long size, int force, gfp_t priority); extern void sock_wfree(struct sk_buff *skb); +extern void skb_orphan_partial(struct sk_buff *skb); extern void sock_rfree(struct sk_buff *skb); extern void sock_edemux(struct sk_buff *skb); diff --git a/net/core/sock.c b/net/core/sock.c index 85e8de1bc7fd..a753d97434dc 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1576,6 +1576,25 @@ void sock_wfree(struct sk_buff *skb) } EXPORT_SYMBOL(sock_wfree); +void skb_orphan_partial(struct sk_buff *skb) +{ + /* TCP stack sets skb->ooo_okay based on sk_wmem_alloc, + * so we do not completely orphan skb, but transfert all + * accounted bytes but one, to avoid unexpected reorders. + */ + if (skb->destructor == sock_wfree +#ifdef CONFIG_INET + || skb->destructor == tcp_wfree +#endif + ) { + atomic_sub(skb->truesize - 1, &skb->sk->sk_wmem_alloc); + skb->truesize = 1; + } else { + skb_orphan(skb); + } +} +EXPORT_SYMBOL(skb_orphan_partial); + /* * Read buffer destructor automatically called from kfree_skb. */ diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index 82f6016d89ab..a6d788d45216 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -412,12 +412,9 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch) /* If a delay is expected, orphan the skb. (orphaning usually takes * place at TX completion time, so _before_ the link transit delay) - * Ideally, this orphaning should be done after the rate limiting - * module, because this breaks TCP Small Queue, and other mechanisms - * based on socket sk_wmem_alloc. */ if (q->latency || q->jitter) - skb_orphan(skb); + skb_orphan_partial(skb); /* * If we need to duplicate packet, then re-insert at top of the -- 2.20.1