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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <503dd37e-aa84-57b5-2473-bb0e0a98d615@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 3/26/19 3:38 PM, Vladimir Oltean wrote: > On 3/27/19 12:13 AM, Florian Fainelli wrote: >> On 3/26/19 3:03 PM, Vladimir Oltean wrote: >>> On 3/26/19 4:31 AM, Florian Fainelli wrote: >>>> >>>> >>>> On 3/23/2019 8:23 PM, Vladimir Oltean wrote: >>>>> In order to support this, we are creating a make-shift switch tag >>>>> out of >>>>> a VLAN trunk configured on the CPU port. Termination on switch ports >>>>> only works when not under a vlan_filtering bridge. We are making >>>>> use of >>>>> the generic CONFIG_NET_DSA_TAG_8021Q code and leveraging it from >>>>> our own >>>>> CONFIG_NET_DSA_TAG_SJA1105. >>>>> >>>>> There are two types of traffic: regular and link-local. >>>>> The link-local traffic received on the CPU port is trapped from the >>>>> switch's regular forwarding decisions because it matched one of the >>>>> two >>>>> DMAC filters for management traffic. >>>>> On transmission, the switch requires special massaging for these >>>>> link-local frames. Due to a weird implementation of the switching >>>>> IP, by >>>>> default it drops link-local frames that originate on the CPU port. It >>>>> needs to be told where to forward them to, through an SPI command >>>>> ("management route") that is valid for only a single frame. >>>>> So when we're sending link-local traffic, we need to clone skb's from >>>>> DSA and send them in our custom xmit worker that also performs SPI >>>>> access. >>>>> >>>>> For that purpose, the DSA xmit handler and the xmit worker communicate >>>>> through a per-port "skb ring" software structure, with a producer >>>>> and a >>>>> consumer index. At the moment this structure is rather fragile >>>>> (ping-flooding to a link-local DMAC would cause most of the frames to >>>>> get dropped). I would like to move the management traffic on a >>>>> separate >>>>> netdev queue that I can stop when the skb ring got full and >>>>> hardware is >>>>> busy processing, so that we are not forced to drop traffic. >>>>> >>>>> Signed-off-by: Vladimir Oltean >>>> >>>> Reviewed-by: Florian Fainelli >>>> >>>> I do like the idea of setting up specific management queue later on, >>>> although it is not clear to me how you would go about integrating it as >>>> a network device, given the DSA slave and master devices, do you know >>>> roughly how you would proceed? >>>> >>> >>> Actually I was thinking about leveraging the multiqueue support that you >>> added in 55199df6d2af ("net: dsa: Allow switch drivers to indicate >>> number of TX queues") and expose the slave netdev .ndo_select_queue >>> callback towards DSA ports. There I would return queue #0 if >>> sja1105_is_link_local(skb), and queue #1 otherwise. >>> Are there any complications that I'm missing? >> >> So that queue could be used to steer management traffic, but it would >> still attempt to perform a dev_queue_xmit() using the master DSA network >> device unless you somehow change that and/or parent that queue to a >> different network device that the sja1105 switch driver creates (which >> is doable). >> > > But the problem I'm trying to solve with the management queue is not > congestion on the master port or inside the switch, but a problem that I > myself have created by putting some skb's in a ring that is finite (and > small) in size: the DSA xmit racing with my xmit worker. Oh I understood that part, which is why I was wondering if it even made sense to make use of a particular queue and the flow control that is offered with that given that this is already quite an ad-hoc solution and what you proposed seems to do the job alright. > Congestion management on the switch is a much ampler issue that I don't > yet know how to handle. The MACs don't appear to generate pause frames, > and the pause frames that they receive are trapped to the CPU as > link-local traffic (DMAC 01-80-C2-00-00-01) where they are simply > consumed by the master's MAC. Woah, okay :) I suppose this can be made to work if you accept loading your host CPU a little bit and have it perform flow control instead of the switch itself. There is no way to have the switch's internal buffering automatically deal with pause frames? -- Florian