netdev - Re: [RFC] net : add tx timestamp to packet mmap.

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Date:	Thu, 13 Dec 2012 19:17:33 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	Paul Chavent <Paul.Chavent@...ra.fr>
Cc:	davem@...emloft.net, edumazet@...gle.com,
	daniel.borkmann@....ee.ethz.ch, xemul@...allels.com,
	ebiederm@...ssion.com, netdev@...r.kernel.org
Subject: Re: [RFC] net : add tx timestamp to packet mmap.

On Thu, Dec 13, 2012 at 05:13:56PM +0100, Paul Chavent wrote:
> >
> >In order for time stamps to appear, somebody has to call
> >skb_tx_timestamp() ...
> Yes. "Somebody" means "the hardware driver" after completing xmit.
> That's true ?

Yes, the MAC driver must call this helper function, but not many
drivers do this yet. You didn't say which MAC driver you are using and
whether it supports Tx SO_TIMESTAMPING or not.

> Yes, it only sets some flags. I thought that those flags was
> required by the skb_tx_timestamp() in order to make the appropriate
> timestamping (hardware, software, etc).
> 
> So in order to have tx timestamp that work, both calls are needed ?

Yes.
 
> Why sock_tx_timestamp is called in packet_fill_skb and
> packet_sendmsg_spkt and not in tpacket_fill_skb ?
> Why i can retrieve timestamps when i add this call ?

Sorry, I don't know much about packet mmap. Last time I tried it, some
years ago, it wasn't really working.

Richard
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