netdev - Re: [PATCH v2 2/3] net_sched: Add accessor function for packet length for qdiscs

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Date:	Fri, 25 Jul 2008 19:46:44 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Jussi Kivilinna <jussi.kivilinna@...et.fi>
Cc:	David Miller <davem@...emloft.net>, kaber@...sh.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH v2 2/3] net_sched: Add accessor function for packet
	length for qdiscs

On Fri, Jul 25, 2008 at 04:15:03PM +0300, Jussi Kivilinna wrote:
> Quoting "Jarek Poplawski" <jarkao2@...il.com>:
...
>> Is it's really needed? Actually, if it's only for stats, I really
>> can't see the reason why not to get this info old way - before
>> enqueing? (And this could be not enough if we want packets count
>> like in htb.)
>>
>
> qdisc_enqueue recalculates packet size if inner qdisc has size table  
> set, so qdisc_pkt_len might return different length after qdisc_enqueue 
> than what it was before.

The question is how much does it matter for statistics. Packets' size
(and number) can change many times in many places. Does it mean all
these places should count the same or "real" size? But, if it's really
necessary here, IMHO, it should be done "clean" way, like additional
parameter(s) to qdisc_enqueue(), because in cases like NET_XMIT_CN we
don't even know what happened with an skb.

Jarek P.
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