netdev - Re: [PATCH 2/7] ATM cell alignment.

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Message-ID: <4801ED79.5090502@andyfurniss.entadsl.com>
Date:	Sun, 13 Apr 2008 12:24:41 +0100
From:	Andy Furniss <lists@...yfurniss.entadsl.com>
To:	Jesper Dangaard Brouer <hawk@...u.dk>
CC:	Stephen Hemminger <stephen.hemminger@...tta.com>,
	netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH 2/7] ATM cell alignment.

Jesper Dangaard Brouer wrote:

> + The align to ATM cells is used for determining the (ATM) SAR
> + alignment overhead at the ATM layer. (SAR = Segmentation And
> + Reassembly).  This is for example needed when scheduling packet on an
> + ADSL connection.  Note that the extra ATM-AAL overhead is _not_
> + included in this calculation. This overhead is added in the kernel
> + before doing the rate table lookup, as this gives better precision
> + (as the table will always be aligned for 48 bytes).

I see overhead is unsigned short. For me using pppoa/vc mux my overhead 
is IP + 10. I am shaping on eth so skb->len is IP+14 hence I need a 
negative overhead.

Recently built a 2.6.25-rc7 and noticed the cell_align has been added 
and the tables jigged. I am (ab)using this at -5 now. Handy that I only 
need to patch TC rather than kernel and I guess I could use other TCs if 
I needed to shape other not atm ifs.

Russel Stuart's patches handled this case IIRC, has it been lost or have 
I missed something (as usual)?

Andy.
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