[net-next,v2,0/3] make skip_sw actually skip software

Message

Asbjørn Sloth Tønnesen March 5, 2024, 2:43 p.m. UTC

Hi,

During development of flower-route[1], which I
recently presented at FOSDEM[2], I noticed that
CPU usage, would increase the more rules I installed
into the hardware for IP forwarding offloading.

Since we use TC flower offload for the hottest
prefixes, and leave the long tail to the normal (non-TC)
Linux network stack for slow-path IP forwarding.
We therefore need both the hardware and software
datapath to perform well.

I found that skip_sw rules, are quite expensive
in the kernel datapath, since they must be evaluated
and matched upon, before the kernel checks the
skip_sw flag.

This patchset optimizes the case where all rules
are skip_sw, by implementing a TC bypass for these
cases, where TC is only used as a control plane
for the hardware path.

Changes from v1:
- Patch 1:
  - Add Reviewed-By from Jiri Pirko
- Patch 2:
  - Move code, to avoid forward declaration (Jiri).
- Patch 3
  - Refactor to use a static key.
  - Add performance data for trapping, or sending
    a packet to a non-existent chain (as suggested by Marcelo).

[1] flower-route
    https://github.com/fiberby-dk/flower-route

[2] FOSDEM talk
    https://fosdem.org/2024/schedule/event/fosdem-2024-3337-flying-higher-hardware-offloading-with-bird/

Asbjørn Sloth Tønnesen (3):
  net: sched: cls_api: add skip_sw counter
  net: sched: cls_api: add filter counter
  net: sched: make skip_sw actually skip software

 include/net/pkt_cls.h     |  9 +++++++++
 include/net/sch_generic.h |  4 ++++
 net/core/dev.c            | 10 ++++++++++
 net/sched/cls_api.c       | 39 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 62 insertions(+)