netdev - Re: An inconsistency/bug in ingress netem timestamps

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Message-Id: <200904151610.43980.alexandre.sidorenko@hp.com>
Date:	Wed, 15 Apr 2009 16:10:43 -0400
From:	Alex Sidorenko <alexandre.sidorenko@...com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: An inconsistency/bug in ingress netem timestamps

On April 15, 2009 03:50:22 pm Jarek Poplawski wrote:

> I agree there is an inconsistency, but it seems 100 ms isn't the
> "right" thing to show here. It shows an internal delay added on ifb by
> any packet scheduler, so probably not what a user usually expects.

Hi Jarek,

thank you for your comments. Yes, I understand that it just looked OK in this 
case even though technically the value was not quite correct.

> > The strange thing is that as soon as there is any ptype_all handler
> > installed, skb->tstamp is updated properly. Unfortunately, my knowledge
> > of TC internals is not good enough to find how exactly this happens.
>
> Isn't it when act_mirred calls dev_queue_xmit with dev_queue_xmit_nit?
> But, as above mentioned, I doubt it's "updated properly" in this case.

I can see that dev_queue_xmit_nit calls net_timestamp(skb) unconditionally. I 
agree that to fix this properly we need to update tstamp in another place 
explicitly (in ifb or netem?).

Thanks,
Alex

-- 
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Alexandre Sidorenko             email: asid@...com
WTEC Linux			Hewlett-Packard (Canada)
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