netdev - Re: Problems obtaining software TX timestamps

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Date:	Wed, 08 Sep 2010 17:12:51 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ingo Kofler <ikofler@....uni-klu.ac.at>
Cc:	netdev@...r.kernel.org
Subject: Re: Problems obtaining software TX timestamps

Le mercredi 08 septembre 2010 à 14:11 +0200, Ingo Kofler a écrit :
> Dear all,
> 
> I am trying to obtain software TX timestamps for a each outgoing packet 
> of an UDP socket. For that purpose I set the SO_TIMESTAMPING socket 
> option to SOF_TIMESTAMPING_TX_SOFTWARE | SOF_TIMESTAMPING_SOFTWARE. The 
> setsockopt call succeeds and also a subsequent getsockopt returns the 
> correct flags. However, if a send a single datagram over the socket and 
> try to fetch the packet as well as its timestamp via the socket's 
> MSG_ERRQUEUE I do not get any information. Rather, the select call waits 
> infinitely on the error queue....
> 
> I hardly found any documentation on this timestamping mechanism except 
> the text file in the kernel source code. All I've figured out is that if 
> I want to have hardware TX timestamps, I'll have to make a further ioctl 
> which requires root permissions to active the hardware timestamping. But 
> this is not what I want... software timestamps are sufficient for me. 

To my knowledge, no driver calls skb_tx_timestamp()

You'll need to tweak your NIC driver to play with this TX timestamps


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