netdev - Re: tbf/htb qdisc limitations

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Message-ID: <AANLkTikQkCcPXtRQGp=MQrjrWtae84VzbENn5x+1yC47@mail.gmail.com>
Date:	Tue, 12 Oct 2010 15:31:48 -0400
From:	Steven Brudenell <steven.brudenell@...il.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: tbf/htb qdisc limitations

> Yes, it's not allowed according to Documentation/HOWTO. Btw, as you
> can see e.g. in sch_hfsc comments, 64-bit division is avoided too.

i see sch_hfsc avoids do_div in critical areas for performance
reasons, but uses it other places. it should still be alright to
do_div in tbf_change and htb_change_class, right? it would be nice to
compute the rtabs in those functions instead of having userspace do
it.

> I can only say there is no versioning, but backward compatibility
> is crucial, so you need to do some tricks or data duplication.
> You could probably try to get opinions about it with an RFC on
> moving tbf and htb schedulers to 64 bits if you're interested
> (decoupling it from your specific burst problem).

my burst problem is the only semi-legitimate motivation i can think
of. the only other possible motivations i can imagine are setting
"limit" to buffer more than 4GB of packets and setting "rate" to
something more than 32 gigabit; both of these seem kind of dubious. is
there something else you had in mind?

looking more at the netlink tc interface: why is it that the interface
for so many qdiscs consists of passing a big options struct as a
single netlink attr, instead of a bunch of individual attrs? this kind
of seems contrary to the extensibility / flexibility spirit of
netlink, and seems to be getting in the way of changing the interface.
maybe i should RFC about this instead ;)
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