On Wed, Sep 1, 2021 at 3:42 AM Toke Høiland-Jørgensen [off-list ref] wrote:

John Fastabend [off-list ref] writes:

quoted

Cong Wang wrote:

quoted

On Tue, Aug 24, 2021 at 4:47 PM Martin KaFai Lau [off-list ref] wrote:

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Please explain more on this.  What is currently missing
to make qdisc in struct_ops possible?

I think you misunderstand this point. The reason why I avoid it is
_not_ anything is missing, quite oppositely, it is because it requires
a lot of work to implement a Qdisc with struct_ops approach, literally
all those struct Qdisc_ops (not to mention struct Qdisc_class_ops).
WIth current approach, programmers only need to implement two
eBPF programs (enqueue and dequeue).

Thanks.

Another idea. Rather than work with qdisc objects which creates all
these issues with how to work with existing interfaces, filters, etc.
Why not create an sk_buff map? Then this can be used from the existing
egress/ingress hooks independent of the actual qdisc being used.

I agree. In fact, I'm working on doing just this for XDP, and I see no
reason why the map type couldn't be reused for skbs as well. Doing it
this way has a couple of benefits:

I do see a lot of reasons, for starters, struct skb_buff is very different
from struct xdp_buff, any specialized map can not be reused. I guess you
are using a generic one, how do you handle the refcnt at least for skb?

- It leaves more flexibility to BPF: want a simple FIFO queue? just
  implement that with a single queue map. Or do you want to build a full
  hierarchical queueing structure? Just instantiate as many queue maps
  as you need to achieve this. Etc.

Please give an example without a queue. ;) Queue is too simple, show us
something more useful please. How do you plan to re-implement EDT with
just queues?

- The behaviour is defined entirely by BPF program behaviour, and does
  not require setting up a qdisc hierarchy in addition to writing BPF
  code.

I have no idea why you call this a benefit, because my goal is to replace
Qdisc's, not to replace any other things. You know there are plenty of Qdisc's
which are not implemented in Linux kernel.

- It should be possible to structure the hooks in a way that allows
  reusing queueing algorithm implementations between the qdisc and XDP
  layers.

XDP has no skb but xdp_buff, no? And again, why only queues?

Thanks.