[PATCH] krt: Dump routing tables separetely on linux to avoid congestion

[Ondrej Zajicek]

On Sat, Apr 16, 2022 at 07:28:59PM +0200, Toke Høiland-Jørgensen wrote:
> Daniel Gröber <dxld at darkboxed.org> writes:
> 
> > When dumping the routing table bird currently doesn't set the rtm_table
> > netlink field to select any particular one but rather wants to get all at
> > once.
> >
> > This can be problematic when multiple routing daemons are running on a
> > system as the kernel's route modification performance goes down
> > drasticly (by a factor of 20-200ish) when the table is being modified while
> > it's being dumped.
> >
> > To avoid this situation we make bird do dumps on a per-kernel-table
> > basis. This then allows the administrator to have multiple routing daemons
> > use different kernel tables which sidesteps the problem.
> >
> > See also this discussion on the babel-users mailing list:
> >   https://alioth-lists.debian.net/pipermail/babel-users/2022-April/003902.html
> 
> Note that this only works with the strict netlink filter checking is
> enabled (i.e., if the setsockopt for NETLINK_GET_STRICT_CHK succeeds).
> Bird currently doesn't check this at runtime at all, so just applying
> this patch as-is will not work correctly on older kernels (<4.20).

Hi

I like the idea of scanning tables independently, but i suspected there
would be an issue on older kernels without NETLINK_GET_STRICT_CHK.
I will check how hard it would be to switch CONFIG_ALL_TABLES_AT_ONCE
in run-time.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."