Re: [PATCH net-next v3] net: ipv4: add support for ECMP hash policy choice

On Mar 15, 2017, at 11:17 AM, Nicolas Dichtel [off-list ref] wrote:

Le 15/03/2017 à 00:45, David Ahern a écrit :

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On 3/14/17 5:27 PM, Stephen Hemminger wrote:

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On Tue, 14 Mar 2017 15:38:40 -0700
Roopa Prabhu [off-list ref] wrote:

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That's what my initial version did, but this was discussed during NetConf in Seville
and it was decided that it's best to make a global sysctl, thus the change.  

Correct, we discussed this, and we all agreed to only have a sysctl for now.  

Why? If you are going to have private discussions please post the rationale
in public.  

Stephen, is there any reason to have a per ecmp route multipath algo
selection ?.
All platforms have a global multipath selection algo. I also don't see
routing daemons ready or willing to specify a per ecmp route multipath
selection algo attribute.  

There is no compelling reason to make the attribute per route. But the
issue is more that configuration through sysctl's is problematic. It doesn't
fit into the standard API paradigm. Sysctl's are like routing patches not
part of the real CLI. Trying to trap sysctl's for things like switchedev
offload is particularly problematic. I can see the case for either way,
and don't have a fixed opinion.  

ok. understand the switchdev offload part. It was that way in the past...but
today you can listen to sysctl updates on the netconf netlink channel.
it works pretty well.

Is there another patch to add the NETCONFA_ECMP support?

does userspace care?

Yes, I think it is needed so that userspace can correctly monitor this behavior.
It also enables to check this parameter through netlink.


Regards,
Nicolas

This doesn’t fit the NETCONFA model well, there is no “all”, “default” or per iface option to be set, also
the other multipath sysctl which affects behaviour doesn’t have a notification.

Thanks,
 Nik