[Cerowrt-devel] some kernel updates

Jesper Dangaard Brouer jbrouer at redhat.com
Tue Aug 27 07:10:23 EDT 2013

On Fri, 23 Aug 2013 13:29:25 -0700
Dave Taht <dave.taht at gmail.com> wrote:

> Does anyone have a date/kernel version on when linklayer overhead
> compensation stopped working?

ADSL/ATM linklayer shaping were broken in kernel release from 3.8 to
3.10 by commit 56b765b79 ("htb: improved accuracy at high rates") in

> There was a bug even prior to 3.8 that looked bad.

Eric Dumazet also found a general "linklayer atm" regression
(dating way-back), which could cause rate-tables to get wrongly shared
between the same rates with-and-without linklayer atm settings.

Addressed/fixed in (3.10-rc6:):
 - commit 40edeff6e1c (net_sched: qdisc_get_rtab() must check data[] array)

When configuring two completely equal rates, the kernel detects that
these two equal rates can share the same rate-table.  But the kernel
didn't check if the rate-table data had been modified, which is done
in the linklayer atm case.

In practice, this often isn't a problem, as overhead parameter is
usually combined with the linklayer parameter.

See my description here:

Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer

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