netdev - Re: [PATCH net-next 6/6] sched: Eliminate use of flow_keys in sch

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Message-ID: <1425324483.5130.115.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 02 Mar 2015 11:28:03 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Florian Westphal <fw@...len.de>
Subject: Re: [PATCH net-next 6/6] sched: Eliminate use of flow_keys in
 sch_sfq


On Mon, 2015-03-02 at 08:25 -0800, Tom Herbert wrote:

> One other possibility is that with the txhash changes we can rehash
> individual connections that are sourced from the host. I was planning
> to do this on too many TCP retransmits to try to get a different ECMP
> path (type of source routing), but we could also do this periodically
> or based on request from qdisc. ooo_okay could be taken into account
> to avoid OOO packets.

About locally generated traffic, skb->txhash potential uses would be

1) Somewhat spray txhash on the wire (Hmmm...)
   Hard to do that with regular IPv4/tcp traffic, or quite hacky.
   (like VLAN spraying...)

2.1) Slave selection on bonding driver
2.2) TX queue selection on multiqueue NIC.

    In this model (way different than XPS), then skb->ooo_okay is of
    no use :

    In both cases, if you change skb->txhash after congestion event,
    you do not care of reorders anyway. They are going to be generated
    most probably because of different paths.



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