Hello folks,
I've discovered two strange behaviours (bugs?) about timestamp
generation:
1. If a program opens an AF_PACKET socket and setup a reception ring
with setsockopt(sock, SOL_PACKET, PACKET_RX_RING), timestamps are
automatically (re)enabled at the reception of every packet.
2. Setting SOL_SOCKET/SO_TIMESTAMP to 0 doesn't disables timestamp
generation. Every skb continues begin timestamped until you close the
socket that activated it.
Timestamp generation is a heavy task that is consuming more than 50% of
the CPU (using ACPI PM clock) and is currently the bottleneck in my
packet capturing application.
The attached patch removes the automatic timestamp activation, that
only mmap'ed AF_PACKET sockets perform. I known it can break user
applications, but I believe that it's the correct solution.
I will be very pleased to receive any feedback.
Signed-off-by: Unai Uribarri <[email protected]>
---
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 1322d62..a4f2da3 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -640,10 +640,6 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, struct packe
h->tp_snaplen = snaplen;
h->tp_mac = macoff;
h->tp_net = netoff;
- if (skb->tstamp.tv64 == 0) {
- __net_timestamp(skb);
- sock_enable_timestamp(sk);
- }
tv = ktime_to_timeval(skb->tstamp);
h->tp_sec = tv.tv_sec;
h->tp_usec = tv.tv_usec;
-
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