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

[David Miller <davem@davemloft.net>]

From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Date: Tue, 14 Mar 2017 17:58:46 +0200

> On 14/03/17 17:55, Stephen Hemminger wrote:
>> On Tue, 14 Mar 2017 17:36:15 +0200
>> Nikolay Aleksandrov <nikolay@cumulusnetworks.com> wrote:
>> 
>>> This patch adds support for ECMP hash policy choice via a new sysctl
>>> called fib_multipath_hash_policy and also adds support for L4 hashes.
>>> The current values for fib_multipath_hash_policy are:
>>>  0 - layer 3 (default)
>>>  1 - layer 4
>>> If there's an skb hash already set and it matches the chosen policy then it
>>> will be used instead of being calculated (currently only for L4).
>>> In L3 mode we always calculate the hash due to the ICMP error special
>>> case, the flow dissector's field consistentification should handle the
>>> address order thus we can remove the address reversals.
>>>
>>> Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
>> 
>> It is good to see ECMP come back from the grave.
>> Linux used to support it long ago but was abandoned after it was unstable
>> and removed from iproute2 in 2012.
>> 
>> The old API was through route attributes which makes more sense than
>> doing it with sysctl. It makes more sense to use netlink instead.
>> Therefore please go back and do something like the old API rather than doing it through
>> sysctl.
>> 
> 
> 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.