netdev - Re: [PATCH ver2] Avoid enqueuing skb for default qdiscs

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Date:	Fri, 7 Aug 2009 08:26:04 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	herbert@...dor.apana.org.au, jarkao2@...il.com, kaber@...sh.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH ver2] Avoid enqueuing skb for default qdiscs

Hi Dave,

David Miller <davem@...emloft.net> wrote on 08/07/2009 02:11:26 AM:

> >  static inline int dev_requeue_skb(struct sk_buff *skb, struct Qdisc
*q)
> >  {
> >     q->gso_skb = skb;
> >     q->qstats.requeues++;
> > +   q->q.qlen++;   /* it's still part of the queue */
> >     __netif_schedule(q);
> >
> >     return 0;
>
> I'm dubious about this new qlen accounting scheme, does it handle
> the non-bypass case properly?  Can you explain how it works
> exactly?

Adding one to qlen will handle non-bypass correctly. On the next
non-bypass (or a bypass) xmit, dequeue_skb will remove gso_skb and
decrement the counter. If no more xmits are done, qdisc_reset will
also fix it. I got this idea by extending one of Jarek's patches:

commit 61c9eaf90081cbe6dc4f389e0056bff76eca19ec
Author: Jarek Poplawski <jarkao2@...il.com>
Date:   Wed Nov 5 16:02:34 2008 -0800
    pkt_sched: Fix qdisc len in qdisc_peek_dequeued()

Thanks,

- KK

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