netdev - Re: Problems obtaining software TX timestamps

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Date:	Thu, 09 Sep 2010 20:58:50 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	Ingo Kofler <ikofler@....uni-klu.ac.at>, netdev@...r.kernel.org
Subject: Re: Problems obtaining software TX timestamps

Le jeudi 09 septembre 2010 à 19:32 +0200, Richard Cochran a écrit :
> On Thu, Sep 09, 2010 at 04:02:38PM +0200, Eric Dumazet wrote:
> > Should drivers call it at start_xmit() time, or at tx completion time ?
> 

> IMHO, it should be done as immediately after the buffer has been
> handed off to the hardware. Not all MACs have a completion method, so
> that would at least make the "rule" consistent.
> 

Well, all drivers must release skb *somewhere*, either in their
ndo_start_xmit() or TX completion ;)

> In general, the goals of high volume and timestamp accuracy are in
> conflict (unless you have HW timestamping). If users are relying on SW
> timestamping, then they should be aware of the fact that high network
> traffic will spoil their fun.
> 

- Full duplex mode wanted
- And small TX rings



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