Hi,
I am continuing the work of ebpf-based Qdisc based on Cong’s previous
RFC. The followings are some use cases of eBPF Qdisc:
1. Allow customizing Qdiscs in an easier way. So that people don't
have to write a complete Qdisc kernel module just to experiment
some new queuing theory.
2. Solve EDT's problem. EDT calcuates the "tokens" in clsact which
is before enqueue, it is impossible to adjust those "tokens" after
packets get dropped in enqueue. With eBPF Qdisc, it is easy to
be solved with a shared map between clsact and sch_bpf.
3. Replace qevents, as now the user gains much more control over the
skb and queues.
4. Provide a new way to reuse TC filters. Currently TC relies on filter
chain and block to reuse the TC filters, but they are too complicated
to understand. With eBPF helper bpf_skb_tc_classify(), we can invoke
TC filters on _any_ Qdisc (even on a different netdev) to do the
classification.
5. Potentially pave a way for ingress to queue packets, although
current implementation is still only for egress.
I’ve combed through previous comments and appreciated the feedbacks.
Some major changes in this RFC is the use of kptr to skb to maintain
the validility of skb during its lifetime in the Qdisc, dropping rbtree
maps, and the inclusion of two examples.
Some questions for discussion:
1. We now pass a trusted kptr of sk_buff to the program instead of
__sk_buff. This makes most helpers using __sk_buff incompatible
with eBPF qdisc. An alternative is to still use __sk_buff in the
context and use bpf_cast_to_kern_ctx() to acquire the kptr. However,
this can only be applied to enqueue program, since in dequeue program
skbs do not come from ctx but kptrs exchanged out of maps (i.e., there
is no __sk_buff). Any suggestion for making skb kptr and helper
functions compatible?
2. The current patchset uses netlink. Do we also want to use bpf_link
for attachment?
3. People have suggested struct_ops. We chose not to use struct_ops since
users might want to create multiple bpf qdiscs with different
implementations. Current struct_ops attachment model does not seem
to support replacing only functions of a specific instance of a module,
but I might be wrong.
Todo:
- Add selftest
- Make bpf list/rbtree use list/rbnode in skb so that developers
don't need to allocate bpf objects for storing skb kptrs.
Note:
- This patchset requires bpf support of exchanging kptr into allocated
objects (local kptr), which Dave Marchevsky is working on.
- The user space programs in the sample are adapted from the example
Peihao Yang written in RFC v5 thread.
---
v7: Reference skb using kptr to sk_buff instead of __sk_buff
Use the new bpf rbtree/link to for skb queues
Add reset and init programs
Add a bpf fq qdisc sample
Add a bpf netem qdisc sample
v6: switch to kptr based approach
v5: mv kernel/bpf/skb_map.c net/core/skb_map.c
implement flow map as map-in-map
rename bpf_skb_tc_classify() and move it to net/sched/cls_api.c
clean up eBPF qdisc program context
v4: get rid of PIFO, use rbtree directly
v3: move priority queue from sch_bpf to skb map
introduce skb map and its helpers
introduce bpf_skb_classify()
use netdevice notifier to reset skb's
Rebase on latest bpf-next
v2: Rebase on latest net-next
Make the code more complete (but still incomplete)
Amery Hung (5):
net_sched: Add reset program
net_sched: Add init program
tools/libbpf: Add support for BPF_PROG_TYPE_QDISC
samples/bpf: Add an example of bpf fq qdisc
samples/bpf: Add an example of bpf netem qdisc
Cong Wang (3):
net_sched: Introduce eBPF based Qdisc
net_sched: Add kfuncs for working with skb
net_sched: Introduce kfunc bpf_skb_tc_classify()
include/linux/bpf_types.h | 4 +
include/uapi/linux/bpf.h | 23 +
include/uapi/linux/pkt_sched.h | 24 ++
kernel/bpf/btf.c | 5 +
kernel/bpf/helpers.c | 1 +
kernel/bpf/syscall.c | 10 +
net/core/filter.c | 100 +++++
net/sched/Kconfig | 15 +
net/sched/Makefile | 1 +
net/sched/sch_bpf.c | 729 ++++++++++++++++++++++++++++++++
samples/bpf/Makefile | 14 +-
samples/bpf/bpf_experimental.h | 134 ++++++
samples/bpf/tc_clsact_edt.bpf.c | 103 +++++
samples/bpf/tc_sch_fq.bpf.c | 666 +++++++++++++++++++++++++++++
samples/bpf/tc_sch_fq.c | 321 ++++++++++++++
samples/bpf/tc_sch_netem.bpf.c | 256 +++++++++++
samples/bpf/tc_sch_netem.c | 347 +++++++++++++++
tools/include/uapi/linux/bpf.h | 23 +
tools/lib/bpf/libbpf.c | 4 +
19 files changed, 2779 insertions(+), 1 deletion(-)
create mode 100644 net/sched/sch_bpf.c
create mode 100644 samples/bpf/bpf_experimental.h
create mode 100644 samples/bpf/tc_clsact_edt.bpf.c
create mode 100644 samples/bpf/tc_sch_fq.bpf.c
create mode 100644 samples/bpf/tc_sch_fq.c
create mode 100644 samples/bpf/tc_sch_netem.bpf.c
create mode 100644 samples/bpf/tc_sch_netem.c
--
2.20.1
