Re: Dropping Packets in 2.6.17

[Arjan van de Ven <arjan@infradead.org>]

On Thu, 2006-06-22 at 04:31 -0700, Danial Thom wrote:
> I'm trying to make a case for using linux as a
> network appliance, but I can't find any
> combination of settings that will keep it from
> dropping packets at an unacceptably high rate.
> The test system is a 1.8Ghz Opteron with intel
> gigE cards running 2.6.17. I'm passing about 70K
> pps through the box, which is a light load, but
> userland activities (such as building a kernel)
> cause it to lose packets, even with backlog set
> to 20000. I had the same problem with 2.6.12 and
> abandoned the effort. Has anything been done
> since to give priority to networking? You can't
> have a network appliance drop packets when some
> application is gathering stats or a user is
> looking at a graph. What tunings are available?

Hi Danial,

the most likely tunable that will help you is

/proc/sys/vm/min_free_kbytes

For the router kind of device that one usually needs bumping a bit;
without the bumping the VM doesn't see enough "normal" activity to tune
it's emergency/interrupt handling buffers (and most networking
allocations happen in interrupt context), and then ends up failing
allocations in interrupt context, which leads to dropped packets.

Greetings,
   Arjan van de Ven

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