netdev - tbf/htb qdisc limitations

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 8 Oct 2010 16:58:36 -0400
From:	Steven Brudenell <steven.brudenell@...il.com>
To:	netdev@...r.kernel.org
Subject: tbf/htb qdisc limitations

hi folks,

i was disappointed recently to find that i can't set the "burst"
parameters very high on the tbf or htb qdiscs. the actual limit of the
burst parameters varies, according to the rate parameter. at the
relatively low rate i want to set, i want to have the burst parameter
be several gigabytes, but i'm actually limited to only a few
megabytes.

(motivation: a fully-automated way to stay inside the monthly transfer
limits imposed by many ISPs these days, without resorting to a
constant rate limit. for example, comcast limits its customers to
250GB/month, which is about 101KB/s; many cellular data plans in the
US limit to 5GB/month =~ 2KB/s).

i'll gladly code a patch, but i'd like the list's advice on whether
this is necessary, and a little bit about how to proceed:

1) what is the purpose of the "rate tables" used in these qdiscs --
why use them in favor of dividing bytes by time to compute a rate? i
assume the answer has something to do with restrictions on using
floating point math (maybe even integer division?) at different places
/ interruptability states in the kernel. maybe this is documented on
kernelnewbies somewhere but i couldn't find it.

2) is there an established procedure for versioning a netlink
interface? today the netlink interface for tbf and htb is horribly
implementation-coupled (the "burst" parameters need to be munged
according to the "rate" parameters and kernel tick rate). i think i
would need to change these interfaces in order to change the
accounting implementation in the corresponding qdisc. however, i
probably want to remain compatible with old userspace.

~steve
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html