quoted

This series introduces tracing infrastructure for AF_XDP sockets (xsk).
A trace event 'xsk_packet_drop' is created which can be enabled by

toggling

quoted

/sys/kernel/debug/tracing/events/xsk/xsk_packet_drop/enable

When enabled and packets or empty packet buffers are dropped in the

kernel,

quoted

traces are generated which describe the reason for the packet drop, the

netdev

quoted

and qid information of the xsk which encountered the drop, and some

more

quoted

information depending on what type of drop was encountered that will tell
the user why the packet was dropped.  This information should help a user
troubleshoot packet drops by providing an extra level of detail which is not
available through use of simple counters

Example traces:
xsk_packet_drop: netdev: ve3213 qid 0 reason: packet too big: len 3000

max 2048 not_used 0

quoted

xsk_packet_drop: netdev: ve3213 qid 0 reason: invalid fill addr: addr 520192

not_used 0 not_used 0

quoted

xsk_packet_drop: netdev: ve9266 qid 0 reason: invalid tx desc: addr 0 len

4097 options 0

quoted

It was decided to use a single event 'xsk_packet_drop' to capture these

three

quoted

drop types. This means that for some of them, there is some redundant

information

quoted

in the trace marked as 'not_used'. An alternative to this would be to

introduce 3

quoted

separate event types under xsk, each with their own appropriate trace

format.

quoted

Suggestions are welcome on which approach would be better to take.

The event can be monitored using perf:
perf stat -a -e xsk:xsk_packet_drop

A selftest is added for each drop type. These tests provide the conditions

to

quoted

trigger the traces and ensure that the appropriate traces are generated.

So what you have done now is to remove all the trace points that
provided no added information on top of the stats counters. The ones
you have left, provide extra information. The two  XSK_TRACE_INVALID_*
points provide the reason why the descriptor was dropped and
XSK_TRACE_DROP_PKT_TOO_BIG provides the size of the packet that was
dropped.

However, the XSK_TRACE_INVALID checks could be performed from user
space and the same data could be printed out from there. A developer
could add this, or we could have a verification mode in the ring
access functions in libbpf that could be turned on by the developer if
he sees the error counters in the kernel being increased. That only
leaves us with XSK_TRACE_DROP_PKT_TOO_BIG which cannot be tested by
user space since the ingress packet is being dropped by the kernel.
But this is unfortunately not enough to warrant this trace
infrastructure on its own, so I think we should drop this patch set.

But I would really like to salvage all your tests, because they are
needed. Instead of verifying the trace, could you please verify the
stats counters that are already there? A lot of your code will be
applicable for that case too. So my suggestion is that you drop this
patch set and  produce a new one that only focuses on selftests for
the XDP_STATISTICS getsockopt. You can add some of the tests you had
in your v2. What do you think?

Thanks for your feedback Magnus. I see your point. If it's possible to do the invalid desc checking in userspace then this probably doesn't belong in the kernel, and keeping the entire tracing infrastructure just for one trace would be too heavy.

I like your suggestion re stats selftests. I'll submit something along those lines.

Thanks,
Ciara

Thank you.

quoted

v4->v5:
* Removed whitespace and renamed struct name in if_xdp.h as suggested

by Song.

quoted

v3->v4:
* Fixed selftest commits with correct logs
* Fixed warnings reported by W=1 build: trace argument types and print

formatting

quoted

v2->v3:
* Removed some traces which traced events which were not technically

drops eg.

quoted

when the rxq is full.
* Introduced traces for descriptor validation on RX and TX and selftests for

both

quoted

v1->v2:
* Rebase on top of Björn's cleanup series.
* Fixed packet count for trace tests which don't need EOT frame.

This series applies on commit

23a2d70c7a2f28eb1a8f6bc19d68d23968cad0ce

quoted

Ciara Loftus (6):
  xsk: add tracepoints for packet drops
  selftests/bpf: restructure setting the packet count
  selftests/bpf: add framework for xsk selftests
  selftests/bpf: XSK_TRACE_DROP_PKT_TOO_BIG test
  selftests/bpf: XSK_TRACE_INVALID_FILLADDR test
  selftests/bpf: XSK_TRACE_INVALID_DESC_TX test

 MAINTAINERS                                |   1 +
 include/linux/bpf_trace.h                  |   1 +
 include/trace/events/xsk.h                 |  71 +++++++
 include/uapi/linux/if_xdp.h                |   6 +
 kernel/bpf/core.c                          |   1 +
 net/xdp/xsk.c                              |   7 +-
 net/xdp/xsk_buff_pool.c                    |   3 +
 net/xdp/xsk_queue.h                        |   4 +
 tools/include/uapi/linux/if_xdp.h          |   6 +
 tools/testing/selftests/bpf/test_xsk.sh    |  90 ++++++++-
 tools/testing/selftests/bpf/xdpxceiver.c   | 206 +++++++++++++++++++--
 tools/testing/selftests/bpf/xdpxceiver.h   |   9 +
 tools/testing/selftests/bpf/xsk_prereqs.sh |   3 +-
 13 files changed, 379 insertions(+), 29 deletions(-)
 create mode 100644 include/trace/events/xsk.h

--
2.17.1