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authorEric Dumazet <edumazet@google.com>2013-07-30 17:55:08 -0700
committerDavid S. Miller <davem@davemloft.net>2013-07-31 14:59:49 -0700
commitf2f872f9272a79a1048877ea14c15576f46c225e (patch)
tree22af2e425ac96068c2d383c052e1d287db867211 /net
parentca4c3fc24e293719fe7410c4e63da9b6bc633b83 (diff)
downloadlinux-f2f872f9272a79a1048877ea14c15576f46c225e.tar.bz2
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 <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/core/sock.c19
-rw-r--r--net/sched/sch_netem.c5
2 files changed, 20 insertions, 4 deletions
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