netdev - Re: [PATCH] pkt_sched: sch_netem: Limit packet re-ordering functionality to tfifo qdisc.

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Message-ID: <48FF4D85.7050700@trash.net>
Date:	Wed, 22 Oct 2008 17:57:57 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	David Miller <davem@...emloft.net>
CC:	jarkao2@...il.com, netdev@...r.kernel.org,
	herbert@...dor.apana.org.au, shemminger@...tta.com
Subject: Re: [PATCH] pkt_sched: sch_netem: Limit packet re-ordering functionality
 to tfifo qdisc.

David Miller wrote:
> From: Jarek Poplawski <jarkao2@...il.com>
> Date: Fri, 17 Oct 2008 22:12:10 +0200
> 
>> pkt_sched: sch_netem: Limit packet re-ordering functionality to tfifo qdisc.
>>
>> After introducing qdisc->ops->peek() method the only remaining user of
>> qdisc->ops->requeue() is netem_enqueue() using this for packet
>> re-ordering. According to Patrick McHardy: "a lot of the functionality
>> of netem requires the inner tfifo anyways and rate-limiting is usually
>> done on top of netem. So I would suggest so either hard-wire the tfifo
>> qdisc or at least make the assumption that inner qdiscs are work-
>> conserving." This patch tries the former.
>>
>> Signed-off-by: Jarek Poplawski <jarkao2@...il.com>
> 
> This is an interesting patch.
> 
> But the thing that strikes me is this: Why don't we just let sch_netem do
> the reordering inside of itself entirely and just get rid of all of this
> ->requeue() business?

I fully agree, keeping all the ->requeue crap around just for this
cornercase doesn't seem like a good decision. Most of the ->requeu

> sch_netem is just a black box, like any other packet scheduler node in
> the tree, and so it can internally do the reordering with a self managed
> packet list or similar.  All of this can be hidden inside of it's ->dequeue()
> with some pkt_sch watchdog timer that fires to prevent stale packets sitting
> in the reorder queue forever.
> 
> Anyways, just and idea and RFC, just like this patch ;-)
> 

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