netdev - Re: qdisc_enqueue, NET_XMIT_SUCCESS and kfree

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Message-ID: <48AAC884.30802@trash.net>
Date:	Tue, 19 Aug 2008 15:20:04 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	David Miller <davem@...emloft.net>, jussi.kivilinna@...et.fi,
	jarkao2@...il.com, netdev@...r.kernel.org
Subject: Re: qdisc_enqueue, NET_XMIT_SUCCESS and kfree_skb

Herbert Xu wrote:
> On Tue, Aug 19, 2008 at 03:08:57PM +0200, Patrick McHardy wrote:
>>> Another possibility would to replace requeue by a peek+force_dequeue
>>> interface, where you can peek at the next packet, and you could then
>>> dequeue that particular packet if you're satisfied.
>> That would be fine for TBF since it only needs to check whether
>> the current packet exceeds the limit and reschedule otherwise.
>> HFSC OTOH really needs to know the length of the next packet for
>> calculating the deadline.
> 
> You mean a peek interface is insufficient for HFSC? Could you
> elaborate?

I might have misunderstood you, but the way I imagine force_dequeue
is that it would give you the packet peeked at, even if a higher
priority packet is available.

But actually I don't understand the use for force_dequeue at all,
assuming ->peek behaves correctly ->dequeue should already hand
out the correct packet.

(Note: Its OK to hand out a different packet if we had a ->enqueue
operation after ->peek since the upper qdisc can just re-peek and
recalculate based on the new highest priority packet).

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