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* [BUG?] the first bind() of an AF_PACKET socket to an interface is slow
@ 2014-03-31 18:43 Tom Gundersen
  2014-03-31 20:16 ` Daniel Borkmann
  0 siblings, 1 reply; 3+ messages in thread
From: Tom Gundersen @ 2014-03-31 18:43 UTC (permalink / raw)
  To: netdev; +Cc: Kay Sievers

[-- Attachment #1: Type: text/plain, Size: 1353 bytes --]

Hi,

I'm observing some strange behavior using bind().

For any given process, and any given interface, the first time I bind
a socket to the interface it takes a very long time. Subsequent binds
to the same interface in the same process are instantaneous.

The time it takes seems independent of the interface, so also affects
the loopback interface, but binding to all interfaces (ifindex=0) is
instantaneous.

It is also peculiar to note that the time it takes to bind is
seemingly randomly chosen on my machine from 9ms, 19ms, 29ms, 39ms,
49ms and 59 ms, but I never observed any other values.

The attached test program illustrates the problem, binding to
ifindex=0 (all) and ifindex=1 (loopback).

Sample run:
# strace -f -T -ebind ./bind
bind(3, {sa_family=AF_PACKET, proto=0x800, if0, pkttype=0x40 /* ? */,
addr(6)={1328, ffffffffffff}, 20) = 0 <0.000036>
bind(3, {sa_family=AF_PACKET, proto=0x800, if0, pkttype=0x40 /* ? */,
addr(6)={1328, ffffffffffff}, 20) = 0 <0.000033>
bind(3, {sa_family=AF_PACKET, proto=0x800, if1, pkttype=0x40 /* ? */,
addr(6)={1328, ffffffffffff}, 20) = 0 <0.059706>
bind(3, {sa_family=AF_PACKET, proto=0x800, if1, pkttype=0x40 /* ? */,
addr(6)={1328, ffffffffffff}, 20) = 0 <0.000111>


Can anyone enlighten me to what is going on? Is this expected behavior
or a bug? Any suggestions for a work-around?

Cheers,

Tom

[-- Attachment #2: bind.c --]
[-- Type: text/x-csrc, Size: 664 bytes --]

#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <string.h>
#include <linux/if_packet.h>
#include <net/ethernet.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <arpa/inet.h>

int main() {
        struct sockaddr_ll ll;
        int s;
	int i;

	for (i = 0; i < 2; i++) {
		s = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));

	        ll.sll_family = AF_PACKET;
	        ll.sll_protocol = htons(ETH_P_IP);
	        ll.sll_ifindex = i;

	        bind(s, (const struct sockaddr *)&ll, sizeof(ll));
	        bind(s, (const struct sockaddr *)&ll, sizeof(ll));
		close(s);
	}

        return 0;
}

^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2014-03-31 21:24 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2014-03-31 18:43 [BUG?] the first bind() of an AF_PACKET socket to an interface is slow Tom Gundersen
2014-03-31 20:16 ` Daniel Borkmann
2014-03-31 21:24   ` Tom Gundersen

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