On Tue, Jun 12, 2018 at 10:49 AM, Florian Fainelli <f.faine...@gmail.com> wrote: > On 06/12/2018 08:18 AM, Alexander Duyck wrote: >> This patch is meant to provide the basic tools needed to allow us to create >> subordinate device traffic classes. The general idea here is to allow >> subdividing the queues of a device into queue groups accessible through an >> upper device such as a macvlan. >> >> The idea here is to enforce the idea that an upper device has to be a >> single queue device, ideally with IFF_NO_QUQUE set. With that being the >> case we can pretty much guarantee that the tc_to_txq mappings and XPS maps >> for the upper device are unused. As such we could reuse those in order to >> support subdividing the lower device and distributing those queues between >> the subordinate devices. > > This is not necessarily a valid paradigm to work with. For instance in > DSA we have IFF_NO_QUEUE devices, but we still expose multiple egress > queues because that is how an application can choose how it wants to get > packets transmitted at the switch level. We have a 1:1 representation > between a queue at the net_device level, and what an egress queue at the > switch level is, so things like buffer reservation etc. can be configured.
I'm not saying that IFF_NO_QUEUE implies that a device is single queue, but in this case we enforce that the upper device has to be a single queue device so that the code in netdev_pick_tx will ignore the XPS and tc_to_txq mappings for that netdev. I had mentioned IFF_NO_QUEUE as a suggestion as that allows us to avoid head-of-line blocking if the lower device starts to apply back-pressure. > I think you should consider that an upper device might want to have a > 1:1 mapping to the lower device's queues and make that permissible. > Thoughts? I had considered that. However the issue becomes that at that point it makes the setup much more rigid. With this approach I can enable and disable the offload without needing to stop the upper device to either create or remove qdiscs. I would much rather keep the upper device generic and leave it to the lower device to populate the rings and such.
