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Message-ID: <1414405781.4492.38.camel@ubuntu-vm-makita>
Date: Mon, 27 Oct 2014 19:29:41 +0900
From: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To: netdev@...r.kernel.org
Cc: Herbert Xu <herbert@...dor.apana.org.au>,
Eric Dumazet <edumazet@...gle.com>
Subject: Poor UDP throughput with virtual devices and UFO
Hi,
I recently noticed sending UDP packets ends up with very poor throughput when
using UFO and virtual devices.
Example configurations are:
- macvlan on vlan
- gre on bridge
With these configurations, the upper virtual devices (macvlan, gre) has the
UFO feature and the lower devices (vlan, bridge) don't have it. UFO packets
will be sent from the upper devices and fragmented on the lower devices.
So, they will be fragmented before entering qdisc.
Since skb_segment() doesn't increase sk_wmem_alloc, the send buffer of a UDP
socket looks almost always empty, and user space can send packets with no limit,
which causes massive drops on qdisc.
I wrote a patch to increase sk_wmem_alloc in skb_segment(), but I'm wondering
if we can do this change since it has been this way for years and only TCP
handles it so far (d6a4a1041176 "tcp: GSO should be TSQ friendly").
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
Average: 0 0.29 0.00 0.76 0.29 0.00 98.66
Average: 1 0.21 0.00 0.33 0.00 0.00 99.45
Average: 2 0.05 0.00 0.12 0.07 0.00 99.76
Average: 3 0.36 0.00 99.64 0.00 0.00 0.00
- 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
Average: 0 0.17 0.00 3.60 0.00 0.00 96.23
Average: 1 0.13 0.00 6.60 0.00 0.00 93.27
Average: 2 0.23 0.00 5.76 0.07 0.00 93.94
Average: 3 0.17 0.00 17.57 0.00 0.00 82.26
The patch (based on net tree) for the test above:
----
Subject: [PATCH net] gso: Inherit sk_wmem_alloc
Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
---
net/core/skbuff.c | 6 +++++-
net/ipv4/tcp_offload.c | 13 ++++---------
2 files changed, 9 insertions(+), 10 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index c16615b..29dc763 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3020,7 +3020,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
len, 0);
SKB_GSO_CB(nskb)->csum_start =
skb_headroom(nskb) + doffset;
- continue;
+ goto set_owner;
}
nskb_frag = skb_shinfo(nskb)->frags;
@@ -3092,6 +3092,10 @@ perform_csum_check:
SKB_GSO_CB(nskb)->csum_start =
skb_headroom(nskb) + doffset;
}
+
+set_owner:
+ if (head_skb->sk)
+ skb_set_owner_w(nskb, head_skb->sk);
} while ((offset += len) < head_skb->len);
/* Some callers want to get the end of the list.
diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
index 5b90f2f..93758a8 100644
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -139,11 +139,8 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
th->check = gso_make_checksum(skb, ~th->check);
seq += mss;
- if (copy_destructor) {
+ if (copy_destructor)
skb->destructor = gso_skb->destructor;
- skb->sk = gso_skb->sk;
- sum_truesize += skb->truesize;
- }
skb = skb->next;
th = tcp_hdr(skb);
@@ -157,11 +154,9 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
* is freed by GSO engine
*/
if (copy_destructor) {
- swap(gso_skb->sk, skb->sk);
- swap(gso_skb->destructor, skb->destructor);
- sum_truesize += skb->truesize;
- atomic_add(sum_truesize - gso_skb->truesize,
- &skb->sk->sk_wmem_alloc);
+ skb->destructor = gso_skb->destructor;
+ gso_skb->destructor = NULL;
+ atomic_sub(gso_skb->truesize, &skb->sk->sk_wmem_alloc);
}
delta = htonl(oldlen + (skb_tail_pointer(skb) -
--
1.8.1.2
--
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