From ac9d8f03b17de0fc6752ba78f65ef95bfef99f6f Mon Sep 17 00:00:00 2001 From: Toshiaki Makita Date: Mon, 27 Oct 2014 10:30:51 -0700 Subject: [PATCH] net: skb_segment() should preserve backpressure This patch generalizes commit 4506b471c706 ("tcp: GSO should be TSQ friendly") to protocols using skb_set_owner_w() TCP uses its own destructor (tcp_wfree) and needs a more complex scheme as explained in commit a1c914392b65 ("tcp: gso: do not generate out of order packets") This allows UDP sockets using UFO to get proper backpressure, thus avoiding qdisc drops and excessive cpu usage. Here are performance test results (macvlan on vlan): - Before # netperf -t UDP_STREAM ... Socket Message Elapsed Messages Size Size Time Okay Errors Throughput bytes bytes secs # # 10^6bits/sec 212992 65507 60.00 144096 1224195 1258.56 212992 60.00 51 0.45 Average: CPU %user %nice %system %iowait %steal %idle Average: all 0.23 0.00 25.26 0.08 0.00 74.43 - After # netperf -t UDP_STREAM ... Socket Message Elapsed Messages Size Size Time Okay Errors Throughput bytes bytes secs # # 10^6bits/sec 212992 65507 60.00 109593 0 957.20 212992 60.00 109593 957.20 Average: CPU %user %nice %system %iowait %steal %idle Average: all 0.18 0.00 8.38 0.02 0.00 91.43 [edumazet] Rewrote patch and changelog. Signed-off-by: Toshiaki Makita Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/core/skbuff.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index c16615bfb61ed..e48e5c02e877d 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3099,6 +3099,16 @@ perform_csum_check: * (see validate_xmit_skb_list() for example) */ segs->prev = tail; + + /* Following permits correct backpressure, for protocols + * using skb_set_owner_w(). + * Idea is to tranfert ownership from head_skb to last segment. + */ + if (head_skb->destructor == sock_wfree) { + swap(tail->truesize, head_skb->truesize); + swap(tail->destructor, head_skb->destructor); + swap(tail->sk, head_skb->sk); + } return segs; err: -- 2.39.5