diff options
author | Willem de Bruijn <willemb@google.com> | 2011-09-30 10:38:28 +0000 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@suse.de> | 2011-11-11 09:36:29 -0800 |
commit | 62d8d0b9b6c459789876335156c56110042f2158 (patch) | |
tree | 145bb8d2e72331f2bf35c2c43975dd72d78de009 | |
parent | 2146d4667b5fbdb0e186ca8bc6d9cbe7ac42dfdc (diff) |
make PACKET_STATISTICS getsockopt report consistently between ring and non-ring
[ Upstream commit 7091fbd82cd5686444ffe9935ed6a8190101fe9d ]
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r-- | net/packet/af_packet.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index c0c3cda1971..fafb96830e7 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -654,7 +654,10 @@ 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)) { |