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 sppend, 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

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. Perf probing confirms this test successfully triggers netpoll_poll_dev() in typical test runs.

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 --- Sending as an RFC for your appreciation, but it dpends on [1] which is stil under review. Once [1] lands, I will send this officially.

Link: https://lore.kernel.org/all/20250611-netdevsim_stat-v1-0-c11b657d96bf@debian... [1] --- tools/testing/selftests/drivers/net/Makefile | 1 + .../testing/selftests/drivers/net/netpoll_basic.py | 201 +++++++++++++++++++++ 2 files changed, 202 insertions(+)

diff --git a/tools/testing/selftests/drivers/net/Makefile b/tools/testing/selftests/drivers/net/Makefile index be780bcb73a3b..70d6e3a920b7f 100644 --- a/tools/testing/selftests/drivers/net/Makefile +++ b/tools/testing/selftests/drivers/net/Makefile @@ -15,6 +15,7 @@ TEST_PROGS := \ netcons_fragmented_msg.sh \ netcons_overflow.sh \ netcons_sysdata.sh \ + netpoll_basic.py \ ping.py \ queues.py \ stats.py \ diff --git a/tools/testing/selftests/drivers/net/netpoll_basic.py b/tools/testing/selftests/drivers/net/netpoll_basic.py new file mode 100755 index 0000000000000..8abdfb2b1eb6e --- /dev/null +++ b/tools/testing/selftests/drivers/net/netpoll_basic.py @@ -0,0 +1,201 @@ +#!/usr/bin/env python3 +# SPDX-License-Identifier: GPL-2.0 + +# This test aims to evaluate the netpoll polling mechanism (as in netpoll_poll_dev()). +# It presents a complex scenario where the network attempts to send a packet but fails, +# prompting it to poll the NIC from within the netpoll TX side. +# +# This has been a crucial path in netpoll that was previously untested. Jakub +# suggested using a single RX/TX queue, pushing traffic to the NIC, and then sending +# netpoll messages (via netconsole) to trigger the poll. `perf` probing of netpoll_poll_dev() +# showed that this test indeed triggers netpoll_poll_dev() once or twice in 10 iterations. + +# Author: Breno Leitao leitao@debian.org + +import errno +import os +import random +import string +import time + +from lib.py import ( + ethtool, + GenerateTraffic, + ksft_exit, + ksft_pr, + ksft_run, + KsftFailEx, + KsftSkipEx, + NetdevFamily, + NetDrvEpEnv, +) + +NETCONSOLE_CONFIGFS_PATH = "/sys/kernel/config/netconsole" +REMOTE_PORT = 6666 +LOCAL_PORT = 1514 +# Number of netcons messages to send. I usually see netpoll_poll_dev() +# being called at least once in 10 iterations. +ITERATIONS = 10 +DEBUG = False + + +def generate_random_netcons_name() -> str: + """Generate a random name starting with 'netcons'""" + random_suffix = "".join(random.choices(string.ascii_lowercase + string.digits, k=8)) + return f"netcons_{random_suffix}" + + +def get_stats(cfg: NetDrvEpEnv, netdevnl: NetdevFamily) -> dict[str, int]: + """Get the statistics for the interface""" + return netdevnl.qstats_get({"ifindex": cfg.ifindex}, dump=True)[0] + + +def set_single_rx_tx_queue(interface_name: str) -> None: + """Set the number of RX and TX queues to 1 using ethtool""" + try: + # This don't need to be reverted, since interfaces will be deleted after test + ethtool(f"-G {interface_name} rx 1 tx 1") + except Exception as e: + raise KsftSkipEx( + f"Failed to configure RX/TX queues: {e}. Ethtool not available?" + ) + + +def create_netconsole_target( + config_data: dict[str, str], + target_name: str, +) -> None: + """Create a netconsole dynamic target against the interfaces""" + ksft_pr(f"Using netconsole name: {target_name}") + try: + ksft_pr(f"Created target directory: {NETCONSOLE_CONFIGFS_PATH}/{target_name}") + os.makedirs(f"{NETCONSOLE_CONFIGFS_PATH}/{target_name}", exist_ok=True) + except OSError as e: + if e.errno != errno.EEXIST: + raise KsftFailEx(f"Failed to create netconsole target directory: {e}") + + try: + for key, value in config_data.items(): + if DEBUG: + ksft_pr(f"Setting {key} to {value}") + with open( + f"{NETCONSOLE_CONFIGFS_PATH}/{target_name}/{key}", + "w", + encoding="utf-8", + ) as f: + # Always convert to string to write to file + f.write(str(value)) + f.close() + + if DEBUG: + # Read all configuration values for debugging + for debug_key in config_data.keys(): + with open( + f"{NETCONSOLE_CONFIGFS_PATH}/{target_name}/{debug_key}", + "r", + encoding="utf-8", + ) as f: + content = f.read() + ksft_pr( + f"{NETCONSOLE_CONFIGFS_PATH}/{target_name}/{debug_key} {content}" + ) + + except Exception as e: + raise KsftFailEx(f"Failed to configure netconsole target: {e}") + + +def set_netconsole(cfg: NetDrvEpEnv, interface_name: str, target_name: str) -> None: + """Configure netconsole on the interface with the given target name""" + config_data = { + "extended": "1", + "dev_name": interface_name, + "local_port": LOCAL_PORT, + "remote_port": REMOTE_PORT, + "local_ip": cfg.addr_v["4"] if cfg.addr_ipver == "4" else cfg.addr_v["6"], + "remote_ip": ( + cfg.remote_addr_v["4"] if cfg.addr_ipver == "4" else cfg.remote_addr_v["6"] + ), + "remote_mac": "00:00:00:00:00:00", # Not important for this test + "enabled": "1", + } + + create_netconsole_target(config_data, target_name) + ksft_pr(f"Created netconsole target: {target_name} on interface {interface_name}") + + +def delete_netconsole_target(name: str) -> None: + """Delete a netconsole dynamic target""" + target_path = f"{NETCONSOLE_CONFIGFS_PATH}/{name}" + try: + if os.path.exists(target_path): + os.rmdir(target_path) + except OSError as e: + raise KsftFailEx(f"Failed to delete netconsole target: {e}") + + +def check_traffic_flowing(cfg: NetDrvEpEnv, netdevnl: NetdevFamily) -> int: + """Check if traffic is flowing on the interface""" + stat1 = get_stats(cfg, netdevnl) + time.sleep(1) + stat2 = get_stats(cfg, netdevnl) + pkts_per_sec = stat2["rx-packets"] - stat1["rx-packets"] + # Just make sure this will not fail even in slow/debug kernels + if pkts_per_sec < 10: + raise KsftFailEx(f"Traffic seems low: {pkts_per_sec}") + if DEBUG: + ksft_pr(f"Traffic per second {pkts_per_sec} ", pkts_per_sec) + + return pkts_per_sec + + +def do_netpoll_flush(cfg: NetDrvEpEnv, netdevnl: NetdevFamily) -> None: + """Print messages to the console, trying to trigger a netpoll poll""" + for i in range(int(ITERATIONS)): + pkts_per_s = check_traffic_flowing(cfg, netdevnl) + with open("/dev/kmsg", "w", encoding="utf-8") as kmsg: + kmsg.write(f"netcons test #{i}: ({pkts_per_s} packets/s)\n") + + +def test_netpoll(cfg: NetDrvEpEnv, netdevnl: NetdevFamily) -> None: + """Test netpoll by sending traffic to the interface and then sending netconsole messages to trigger a poll""" + target_name = generate_random_netcons_name() + ifname = cfg.dev["ifname"] + traffic = None + + try: + set_single_rx_tx_queue(ifname) + traffic = GenerateTraffic(cfg) + check_traffic_flowing(cfg, netdevnl) + set_netconsole(cfg, ifname, target_name) + do_netpoll_flush(cfg, netdevnl) + finally: + if traffic: + traffic.stop() + delete_netconsole_target(target_name) + + +def check_dependencies() -> None: + """Check if the dependencies are met""" + if not os.path.exists(NETCONSOLE_CONFIGFS_PATH): + raise KsftSkipEx( + f"Directory {NETCONSOLE_CONFIGFS_PATH} does not exist. CONFIG_NETCONSOLE_DYNAMIC might not be set." + ) + + +def main() -> None: + """Main function to run the test""" + check_dependencies() + netdevnl = NetdevFamily() + with NetDrvEpEnv(__file__, nsim_test=True) as cfg: + ksft_run( + [test_netpoll], + args=( + cfg, + netdevnl, + ), + ) + ksft_exit() + + +if __name__ == "__main__": + main()

--- base-commit: 5d6d67c4cb10a4b4d3ae35758d5eeed6239afdc8 change-id: 20250612-netpoll_test-a1324d2057c8

Best regards,