[LARTC] Re: [PATCH 0/2] NET: Accurate packet scheduling for ATM/ADSL

[Russell Stuart]

On Tue, 2006-07-04 at 15:29 +0200, Patrick McHardy wrote:
> Unfortunately I still didn't got to cleaning them up, so I'm sending
> them in their preliminary state. Its not much that is missing, but
> the netem usage of skb->cb needs to be integrated better, I failed
> to move it to the qdisc_skb_cb so far because of circular includes.

Cleanups aside, architecturally the bulk of your patch 
looks like a no-brainier to me.  The calculation of
packet length should be in one place.  Caching it in
skb->cb was a nice touch.

> But nothing unfixable. I'm mostly interested if the current size-tables
> can express what you need for ATM, I wasn't able to understand the
> big comment in tc_core.c in your patch.

Unfortunately you do things in the wrong order for ATM.
See: http://mailman.ds9a.nl/pipermail/lartc/2006q1/018314.html
for an overview of the problem, and then the attached email for
a detailed description of how the current patch addresses it.
It is a trivial fix.

As I said earlier, RTAB and STAB contain the same numbers,
just scaled differently.  The ATM patch stuffed around with
RTAB.  With your patch in place it will have to do the same 
exactly the same thing with STAB - because RTAB and STAB
carry the same data.  So to me the two patches seem
orthogonal.

One observation is the size optimisation you applied to STAB, 
making it variable length, could also be applied to RTAB.  
In fact it should be.  Then they would be identical, apart 
from the scaling.  Even the lookup operation (performed in
qdisc_init_len in your patch) would be identical.

However, now you lot have made me go away and think, I have
another idea on how to attack this.  Perhaps it will be
more palatable to you.  It would replace RTAB and STAB with
a 28 byte structure for most protocol stacks - well all I can
think of off the top of my head, anyway.  RTAB would have to
remain for backwards compatibility, of course.

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From: Russell Stuart <russell at stuart.id.au>
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