Re: time stamps of skb packets in NF_HOOKS callbacks

On Fri, Aug 18, 2006 at 08:43:08AM +0300, John Que (qwejohn@gmail.com) wrote:

Following your answer I tried adding a call to net_enable_timestamp() in
a module I wrote which use NF_HOOKS.
This is what is done , for example, in ipq_rcv_skb(struct sk_buff *skb)
in linux-2.6.14 in net/ipv4/netfilter/ip_queue.c.

After doing so I get timestamps which are not 0.

what I wonder now is :
1) does this have ANY performance implication (when dealing with a
high  network  load which can get to 50,000 packets per second?

Yes, it has. do_gettimeofday() is quite slow on some processors and is
not SMP-friendly.

2) It does work as I said, but I want to be cautios: Am I permitted to
add this method ? are  there any  implications for adding this method
which can create troubles ?
I must say that I am NOT changing anywhere the timestamp; it's only
for statistics.

If you add ata least on socket with SO_TIMESTAMP option, it will enable
timestamps for all skbs, so you have not created any wrong thing, except
that slowed down your network processing.

Regards,
John

-- 
	Evgeniy Polyakov