netdev - Re: [RFC net-next 0/8] net: dsa: Multi-queue awareness

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Message-ID: <20170901000502.GB28960@lunn.ch>
Date:   Fri, 1 Sep 2017 02:05:02 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     netdev@...r.kernel.org, jiri@...nulli.us, jhs@...atatu.com,
        davem@...emloft.net, xiyou.wangcong@...il.com,
        vivien.didelot@...oirfairelinux.com
Subject: Re: [RFC net-next 0/8] net: dsa: Multi-queue awareness

On Wed, Aug 30, 2017 at 05:18:44PM -0700, Florian Fainelli wrote:
> This patch series is sent as reference, especially because the last patch
> is trying not to be creating too many layer violations, but clearly there
> are a little bit being created here anyways.
> 
> Essentially what I am trying to achieve is that you have a stacked device which
> is multi-queue aware, that applications will be using, and for which they can
> control the queue selection (using mq) the way they want. Each of each stacked
> network devices are created for each port of the switch (this is what DSA
> does). When a skb is submitted from say net_device X, we can derive its port
> number and look at the queue_mapping value to determine which port of the
> switch and queue we should be sending this to. The information is embedded in a
> tag (4 bytes) and is used by the switch to steer the transmission.
> 
> These stacked devices will actually transmit using a "master" or conduit
> network device which has a number of queues as well. In one version of the
> hardware that I work with, we have up to 4 ports, each with 8 queues, and the
> master device has a total of 32 hardware queues, so a 1:1 mapping is easy. With
> another version of the hardware, same number of ports and queues, but only 16
> hardware queues, so only a 2:1 mapping is possible.
> 
> In order for congestion information to work properly, I need to establish a
> mapping, preferably before transmission starts (but reconfiguration while
> interfaces are running would be possible too) between these stacked device's
> queue and the conduit interface's queue.
> 
> Comments, flames, rotten tomatoes, anything!

Right, i think i understand.

This works just for traffic between the host and ports.  The host can
set the egress queue. And i assume the queues are priorities, either
absolute or weighted round robin, etc.

But this has no effect on traffic going from port to port. At some
point, i expect you will want to offload TC for that.

How will the two interact? Could the TC rules also act on traffic from
the host to a port? Would it be simpler in the long run to just
implement TC rules?

	  Andrew