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authorWillem de Bruijn <willemb@google.com>2011-09-30 10:38:28 +0000
committerDavid S. Miller <davem@davemloft.net>2011-10-03 14:18:26 -0400
commit7091fbd82cd5686444ffe9935ed6a8190101fe9d (patch)
tree8414bd888e6ef13f9338458ee94cf24b0d34bd2c /net
parentd0e5d83284dac15c015bb48115b6780f5a6413cd (diff)
downloadlinux-linaro-precise-7091fbd82cd5686444ffe9935ed6a8190101fe9d.tar.gz
make PACKET_STATISTICS getsockopt report consistently between ring and non-ring
This is a minor change. Up until kernel 2.6.32, getsockopt(fd, SOL_PACKET, PACKET_STATISTICS, ...) would return total and dropped packets since its last invocation. The introduction of socket queue overflow reporting [1] changed drop rate calculation in the normal packet socket path, but not when using a packet ring. As a result, the getsockopt now returns different statistics depending on the reception method used. With a ring, it still returns the count since the last call, as counts are incremented in tpacket_rcv and reset in getsockopt. Without a ring, it returns 0 if no drops occurred since the last getsockopt and the total drops over the lifespan of the socket otherwise. The culprit is this line in packet_rcv, executed on a drop: drop_n_acct: po->stats.tp_drops = atomic_inc_return(&sk->sk_drops); As it shows, the new drop number it taken from the socket drop counter, which is not reset at getsockopt. I put together a small example that demonstrates the issue [2]. It runs for 10 seconds and overflows the queue/ring on every odd second. The reported drop rates are: ring: 16, 0, 16, 0, 16, ... non-ring: 0, 15, 0, 30, 0, 46, 0, 60, 0 , 74. Note how the even ring counts monotonically increase. Because the getsockopt adds tp_drops to tp_packets, total counts are similarly reported cumulatively. Long story short, reinstating the original code, as the below patch does, fixes the issue at the cost of additional per-packet cycles. Another solution that does not introduce per-packet overhead is be to keep the current data path, record the value of sk_drops at getsockopt() at call N in a new field in struct packetsock and subtract that when reporting at call N+1. I'll be happy to code that, instead, it's just more messy. [1] http://patchwork.ozlabs.org/patch/35665/ [2] http://kernel.googlecode.com/files/test-packetsock-getstatistics.c Signed-off-by: Willem de Bruijn <willemb@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/packet/af_packet.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index c698cec0a44..fabb4fafa28 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -961,7 +961,10 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev,
return 0;
drop_n_acct:
- po->stats.tp_drops = atomic_inc_return(&sk->sk_drops);
+ spin_lock(&sk->sk_receive_queue.lock);
+ po->stats.tp_drops++;
+ atomic_inc(&sk->sk_drops);
+ spin_unlock(&sk->sk_receive_queue.lock);
drop_n_restore:
if (skb_head != skb->data && skb_shared(skb)) {