netdev - Re: [PATCH net-next-2.6] net: force a fresh timestamp for ingress packets

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Message-ID: <1292542305.2655.25.camel@edumazet-laptop>
Date:	Fri, 17 Dec 2010 00:31:45 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Changli Gao <xiaosuo@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net-next-2.6] net: force a fresh timestamp for ingress
 packets

Le jeudi 16 décembre 2010 à 23:42 +0100, Jarek Poplawski a écrit :
> On Thu, Dec 16, 2010 at 11:26:03PM +0100, Eric Dumazet wrote:
> > Le jeudi 16 décembre 2010 ?? 23:08 +0100, Jarek Poplawski a écrit :
> > 
> > > Hmm... Do you expect more people start debugging SFQ or I missed your
> > > point? ;-) Maybe such a change would be reasonable on a cloned skb?
> > 
> > My point was to permit an admin to check his ingress shaping works or
> > not. In this respect, netem was a specialization of a general problem.
> > 
> > We had a prior discussion on timestamping skb in RX path, when RPS came
> > in : Should we take timestamp before RPS or after. At that time we added
> > a sysctl. Not sure it was the right choice :-(
> > 
> > I feel tcpdump (on TX side) should really display time of packet right
> > before being given to device, but this is probably a matter of taste.
> 
> It might be reasonable unless it changes data for later users. That's
> why I mentioned cloning.
> 
> > 
> > Before commit 8caf153974f2 (net: sch_netem: Fix an inconsistency in
> > ingress netem timestamps.), this is what was done.
> 
> Then why don't you try to let turn it off in netem, where it only
> matters?
> 

Because, if you read again my patch, you'll see :

#ifdef CONFIG_NET_CLS_ACT
       if (!skb->tstamp.tv64 || (G_TC_FROM(skb->tc_verd) & AT_INGRESS))
                net_timestamp_set(skb);
#else

So : 

If we are handling an INGRESS packet, we force a timestamp renew.

Therefore :

We dont need in netem_dequeue() to force :

-#ifdef CONFIG_NET_CLS_ACT
-                       /*
-                        * If it's at ingress let's pretend the delay is
-                        * from the network (tstamp will be updated).
-                        */
-                       if (G_TC_FROM(skb->tc_verd) & AT_INGRESS)
-                               skb->tstamp.tv64 = 0;
-#endif

Since :

We are going to renew timestamp anyway.

Conclusion :

I am eliminating dead code.

Is that OK ?

Thanks


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