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ip_input.c / time measurements

To: netdev@xxxxxxxxxxx
Subject: ip_input.c / time measurements
From: Guilhem Tardy <guilhem_tardy@xxxxxxxxx>
Date: Mon, 20 Aug 2001 09:50:42 -0700 (PDT)
Sender: owner-netdev@xxxxxxxxxxx

I am trying to make some measurement of the delays in the IP stack by adding
time values inside UDP packets received on a special port. I intend to hack
into the xmit function of a particular net driver, as in parts of the
ip_input.c file. What is in your opinion the first function of ip_input invoked
upon reception of a packet, and the last before passing to higher protocols? I
thought of ip_rcv(), where incidentally iph = skb->nh.iph; is performed twice
(unnecessarily?), and ip_local_deliver_finish().
Besides, I was a bit confused by the choice of a common time measure for the
kernel parts and the application. Using jiffies limits me to 1/100 of a second
measurement, unless I change that to 1/1000 or less in param.h ! Is there a
more precise variable or function that I could invoke to get exact timings?

Thanks for your help!


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