Re: [PATCH net-next v2 4/4] selftests: net: add netpoll basic functionality test

Breno Leitao wrote:

Add a basic selftest for the netpoll polling mechanism, specifically targeting the netpoll poll() side.

The test creates a scenario where network transmission is running at maximum speed, and netpoll needs to poll the NIC. This is achieved by:

1. Configuring a single RX/TX queue to create contention
2. Generating background traffic to saturate the interface
3. Sending netconsole messages to trigger netpoll polling
4. Using dynamic netconsole targets via configfs
5. Delete and create new netconsole targets after some messages
6. Start a bpftrace in parallel to make sure netpoll_poll_dev() is called
7. If bpftrace exists and netpoll_poll_dev() was called, stop.

The test validates a critical netpoll code path by monitoring traffic flow and ensuring netpoll_poll_dev() is called when the normal TX path is blocked.

This addresses a gap in netpoll test coverage for a path that is tricky for the network stack.

Signed-off-by: Breno Leitao leitao@debian.org

+def bpftrace_call() -> None:

• """Call bpftrace to find how many times netpoll_poll_dev() is called.
• Output is saved in the global variable `maps`"""
• # This is going to update the global variable, that will be seen by the
• # main function
• global MAPS # pylint: disable=W0603
• # This will be passed to bpftrace as in bpftrace -e "expr"
• expr = "BEGIN{ @hits = 0;} kprobe:netpoll_poll_dev { @hits += 1; }"

Is that BEGIN statement needed? I generally just use count().

• MAPS = bpftrace(expr, timeout=BPFTRACE_TIMEOUT, json=True)
• logging.debug("BPFtrace output: %s", MAPS)

+def bpftrace_start():

• """Start a thread to call `call_bpf` in parallel for 2 seconds."""

Stale comment? BPFTRACE_TIMEOUT is set to 15.

• global BPF_THREAD # pylint: disable=W0603
• BPF_THREAD = threading.Thread(target=bpftrace_call)
• BPF_THREAD.start()
• if not BPF_THREAD.is_alive():

•    raise KsftSkipEx("BPFtrace thread is not alive. Skipping test")