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

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Message-Id: <20090417.050422.134655407.davem@davemloft.net>
Date:	Fri, 17 Apr 2009 05:04:22 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jarkao2@...il.com
Cc:	alexandre.sidorenko@...com, netdev@...r.kernel.org,
	shemminger@...tta.com
Subject: Re: An inconsistency/bug in ingress netem timestamps

From: Jarek Poplawski <jarkao2@...il.com>
Date: Thu, 16 Apr 2009 23:48:46 +0200

> David Miller wrote, On 04/16/2009 12:10 PM:
> 
>> Since IFB completely bypasses netif_rx() and netif_receive_skb() I
>> think it should unconditionally set skb->tstamp.tv64 to zero and
>> invoke net_timestamp()
> 
> IFB calls netif_rx() and I don't understand why do we need to update
> tstamp again except for this netem case.
> 
>> This would match the behavior of loopback and tunnels, and in my
>> opinion this is reasonable.  There will be virtually no overhead
>> added unless timestamping is enabled via ping or similar, and in
>> return we get what I think is correctness :-)
> 
> I think we need some consistency in counting or not counting packet
> scheduling delays into timestamps. Anyway we should avoid unnecessary
> updates like now, so I'm proposing something different (for testing).

Ok, now I understand this situation even more clearly, thanks
Jarek.

I think your patch is the most palatable solution I've seen
so far, but I want to consider it some more.

Meanwhile, Alexandre can you test Jarek's patch for your case?

Thanks!
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