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

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Date:   Tue, 14 Mar 2017 17:58:46 +0200
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        roopa@...ulusnetworks.com, dsa@...ulusnetworks.com,
        jkbs@...hat.com, edumazet@...gle.com, pch@...bogen.com
Subject: Re: [PATCH net-next v3] net: ipv4: add support for ECMP hash policy
 choice

On 14/03/17 17:55, Stephen Hemminger wrote:
> On Tue, 14 Mar 2017 17:36:15 +0200
> Nikolay Aleksandrov <nikolay@...ulusnetworks.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@...ulusnetworks.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.

Thanks,
 Nik