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

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Date:	Thu, 16 Dec 2010 22:30:39 +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 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...


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