netdev - Re: [PATCHv2 1/3] NET_SCHED: PSPacer qdisc module

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Date:	Wed, 28 Nov 2007 01:57:04 +0900 (JST)
From:	Ryousei Takano <takano-ryousei@...t.go.jp>
To:	kaber@...sh.net
Cc:	netdev@...r.kernel.org, shemminger@...ux-foundation.org,
	dada1@...mosbay.com, t.kudoh@...t.go.jp
Subject: Re: [PATCHv2 1/3] NET_SCHED: PSPacer qdisc module

> One more thing: your qdisc can only be used as root qdisc since it
> produces packets itself and thereby violates the rule that a qdisc
> can only hand out packets that were previously enqueued to it.
> Using it as a leaf qdisc can make the upper qdiscs qlen counter
> go negative, causing infinite dequeue-loops, so you should make
> sure that its only possibly to use as root qdisc by checking the
> parent. It would also be better to do something like netem
> (enqueue produced packets at the root) to make sure the qlen
> counter is always accurate.
> 
I agree with you.
PSPacer should not use with other rate regulation qdiscs. But, 
I think that a combination of netem and PSPacer is a useful for
emulating networks. The following paper describes experimental
results using PSPacer with netem:

       "Large Scale Gigabit Emulated Testbed for Grid Transport
       Evaluation", PFLDnet 2006.
       http://www.hpcc.jp/pfldnet2006/paper/s1_02.pdf

Best regards,
Ryousei Takano
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