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

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

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")
> +
> +