On Tue, Oct 29, 2019 at 10:03 PM Eric Dumazet [off-list ref] wrote:

On 10/29/19 11:35 AM, Nikolay Aleksandrov wrote:

quoted

Hi Matteo,
Wouldn't it be more useful and simpler to use some field to choose the slave (override the hash
completely) in a deterministic way from user-space ?
For example the mark can be interpreted as a slave id in the bonding (should be
optional, to avoid breaking existing setups). ping already supports -m and
anything else can set it, this way it can be used to do monitoring for a specific
slave with any protocol and would be a much simpler change.
User-space can then implement any logic for the monitoring case and as a minor bonus
can monitor the slaves in parallel. And the opposite as well - if people don't want
these balanced for some reason, they wouldn't enable it.

I kind of agree giving user more control. But I do not believe we need to use the mark
(this might be already used by other layers)

TCP uses sk->sk_hash to feed skb->hash.

Anything using skb_set_owner_w() is also using sk->sk_hash if set.

So presumably we could add a generic SO_TXHASH socket option to let user space
read/set this field.

Hi Eric,

this would work for locally generated echoes, but what about forwarded packets?
The point behind my changeset is to provide consistent results within
a session by using the same path for request and response,
but avoid all sessions flowing to the same path.
This should resemble what happens with TCP and UDP: different
connections, different port, probably a different path. And by doing
this in the flow dissector, other applications could benefit it.

Also, this should somewhat balance the traffic of a router forwarding
those packets. Maybe it's not so much in percentage, but in some
gateways be a considerable volume.

Regards,
-- 
Matteo Croce
per aspera ad upstream