On 6 April 2017 at 15:36, David Ahern <dsa@cumulusnetworks.com> wrote:

net-next tree has the patch set increasing number of labels. Allows up
to 30 labels for ingress (ip->mpls) and routing (mpls->mpls).

An mpls_route is limited to 4096 bytes (number of nexthops + labels); an
lwt (ingress) route is under 128 bytes. With the latest set users of
N-labels takes the performance hit of each additional label.

I think that having 30 stacked labels is useless, regardless of the performance
issue, like Jeff said, the worst case covers 5 labels. I don't inderstand this waste.

On 3/23/17 1:34 PM, Amine Kherbouche wrote:
> Olivier,
>
> The best for me, is to have the possibility to recompile the MPLS
> kernel module with the new value the MAX_LABEL_STACK and then let
> our Segment Routing implementation read this value to determine
> what's feasible.
>
> Yes but we still need a default value.
> You have also to see the perf impact, now the current mpls entry size in
> linux kernel is under
> a cache line, even using 12 stacked labels, we are always under a cache
> line but beyond
> this value we're going to see performance issue.
>

Amine