Re: [Linuxptp-users] Fw: “Resource temporarily unavailable” errors during flood ping test

[Richard C. <ric...@gm...>]

On Tue, Oct 30, 2012 at 06:23:53PM +0100, Richard Cochran wrote:
> On Tue, Oct 30, 2012 at 09:54:30AM -0700, Jacob Keller wrote:
> > 
> > I believe the true correct answer is to completely re-architect the 
> > tx_hwtstamp to be asynchronous, so that it just waits until it receives 
> > the timestamp for a complete sequence of events. That design is 
> > significantly more difficult to write though.
> 
> But even if we did that way, it would not really be a better
> solution. Think about your own Intel cards. They would end up missing
> Tx time stamps and possibly mixing them up due to the hardware
> limitation of having a Tx time stamp FIFO of depth one.

This may be the wrong list, but this reminds me of an issue with the
Intel hardware that I have been meaning to ask you about.  The igb
driver has always had the following comment regarding transmit time
stamps:

 * If we were asked to do hardware stamping and such a time stamp is
 * available, then it must have been for this skb here because we only
 * allow only one such packet into the queue.

This statement wasn't actually true up until recently, when Matthew
Vick added some code that enforced the one packet limit.

If I am not mistaken, the ixgb also would need some kind of guard
against the case when a user program sends two or more event packets
in a row, would it not?

Thanks,
Richard