selftests: drv-net: support generating iperf3 load

While we are not very interested in testing performance
it's useful to be able to generate a lot of traffic.
iperf is the simplest way of getting relatively high PPS.

Reviewed-by: Willem de Bruijn <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

tools/testing/selftests/drivers/net/lib/py/__init__.py

···
     sys.exit(4)
 
 from .env import *
+from .load import *
 from .remote import Remote

tools/testing/selftests/drivers/net/lib/py/load.py

···
+# SPDX-License-Identifier: GPL-2.0
+
+import time
+
+from lib.py import ksft_pr, cmd, ip, rand_port, wait_port_listen
+
+class GenerateTraffic:
+    def __init__(self, env):
+        env.require_cmd("iperf3", remote=True)
+
+        self.env = env
+
+        port = rand_port()
+        self._iperf_server = cmd(f"iperf3 -s -p {port}", background=True)
+        wait_port_listen(port)
+        time.sleep(0.1)
+        self._iperf_client = cmd(f"iperf3 -c {env.addr} -P 16 -p {port} -t 86400",
+                                 background=True, host=env.remote)
+
+        # Wait for traffic to ramp up
+        pkt = ip("-s link show dev " + env.ifname, json=True)[0]["stats64"]["rx"]["packets"]
+        for _ in range(50):
+            time.sleep(0.1)
+            now = ip("-s link show dev " + env.ifname, json=True)[0]["stats64"]["rx"]["packets"]
+            if now - pkt > 1000:
+                return
+            pkt = now
+        self.stop(verbose=True)
+        raise Exception("iperf3 traffic did not ramp up")
+
+    def stop(self, verbose=None):
+        self._iperf_client.process(terminate=True)
+        if verbose:
+            ksft_pr(">> Client:")
+            ksft_pr(self._iperf_client.stdout)
+            ksft_pr(self._iperf_client.stderr)
+        self._iperf_server.process(terminate=True)
+        if verbose:
+            ksft_pr(">> Server:")
+            ksft_pr(self._iperf_server.stdout)
+            ksft_pr(self._iperf_server.stderr)