On 13/08/15 03:07, roopa wrote:
On 8/12/15, 10:30 AM, Robert Shearman wrote:
On 11/08/15 22:45, Roopa Prabhu wrote:
From: Roopa Prabhu <ro...@cumulusnetworks.com>
This patch series adds multipath support to mpls routes.
resembles ipv4 multipath support. The multipath route nexthop
selection algorithm is the same code as in ipv4 fib code.
I understand that the multipath algorithm in ipv4 is undergoing
some changes and will move mpls to similar algo if applicable once
those get merged.
Is it necessary for the mpls patch selection algorithm to closely
resemble the ipv4 one?
No, It is not necessary. I picked that because it was already there. And
I see that ipv4 is also getting some new multipath algorithms
(https://marc.info/?l=linux-api&m=143457208315573&w=2). I wanted to move
to the new RT_MP infra if that becomes applicable in the future.
The MPLS code doesn't have the binary compatibility requirement that the
IPv4 path does, so there isn't so much of a need for the algorithm to be
configurable, provided the default is reasonable. Unless you have a use
case in mind that would particularly suited to the round-robin algorithm?
A flow based algorithm would be much better for traffic that is
sensitive to re-ordering (e.g TCP, L2VPN) and IMHO we should do this
from the start for MPLS.
I've also been looking at implementing this functionality. I've got a
set of patches for this that I can send if you'd like.
Definitely. But, It seems like you can also submit incremental patches
to mine. You can replace the current algo with a hash based with your
patches.
With a flow-based algorithm if there's no need to support weighted paths
then there's no need to iterate through the nexthops to work out which
one should be used and, therefore, there is a performance benefit.
So my patches implement a flow-based path selection without support for
weighted paths. This is similar way to how the IPv6 path selection
works. The user can still do UCMP with this mechanism, but they have to
add the same nexthop multiple times. I don't know if this trade-off is
worth it, but the benefit is that we can always add support for weighted
paths in the future, whereas removing support for weighted paths would
be harder due to compatibility concerns.
Therefore, if I rebased my patches on top of yours I would be removing
code managing the weighting that you will have just added. Not sure if
that is desirable.
If that does not work for you and if you want me to merge with this
series that works too.
I think that would work better. I'll send you a patch against your
current series.
Thanks,
Rob
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