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

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Message-ID: <20101216220838.GB2191@del.dom.local>
Date:	Thu, 16 Dec 2010 23:08:38 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Eric Dumazet <eric.dumazet@...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

On Thu, Dec 16, 2010 at 10:30:39PM +0100, Eric Dumazet wrote:
> Le jeudi 16 décembre 2010 ?? 22:17 +0100, Jarek Poplawski a écrit :
> > On Wed, Dec 15, 2010 at 04:50:52PM +0100, Eric Dumazet wrote:
> > > In commit 8caf153974f2 (net: sch_netem: Fix an inconsistency in ingress
> > > netem timestamps.), Jarek added a logic to refresh timestamps of
> > > ingressed packets going through netem.
> > > 
> > > I believe we should generalize this, forcing a refresh of timestamps in
> > > dev_queue_xmit_nit() for all ingress packets, whatever qdisc/class they
> > > used before being delivered.
> > > 
> > > This way, we can have a good idea when packets are delivered to our
> > > stack (tcpdump -i ifb0), while a tcpdump on original device gives
> > > timestamps right before ingressing.
> > 
> > I don't think we should do it. IMHO netem on ingress is a special case,
> > obviously for testing, and otherwise the real (first) timestamp might
> > be valuable for some users.
> 
> Well, I find difficult to check sfq is actually correctly working
> because timestamps are mixed.
> 
> After this patch, I found the SFQ allot error for example.
> 
> I dont know, I feel adding a sysctl like netdev_tstamp_prequeue is not
> worth it...

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?

Jarek P. 
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