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

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Date:   Tue, 14 Mar 2017 13:25:06 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     David Miller <davem@...emloft.net>
Cc:     nikolay@...ulusnetworks.com, netdev@...r.kernel.org,
        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 Tue, 14 Mar 2017 11:48:37 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:

> From: Nikolay Aleksandrov <nikolay@...ulusnetworks.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@...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.  
> 
> 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.