refactor(tests): don't reuse iperf on the host

Similar to the RX tests, in TX tests we can just use
one shot servers on the host. This should prevent any
instability with host iperf caused by reuse.

Signed-off-by: Egor Lazarchuk <yegorlz@amazon.co.uk>

Author: ShadowCurse

tests/integration_tests/performance/test_rate_limiter.py

@@ -139,9 +139,6 @@ def _check_tx_rate_limiting(test_microvm):
     eth1 = test_microvm.iface["eth1"]["iface"]
     eth2 = test_microvm.iface["eth2"]["iface"]
 
-    # Start iperf server on the host as this is the tx rate limiting test.
-    _start_iperf_server_on_host(test_microvm.netns.cmd_prefix())
-
     # First step: get the transfer rate when no rate limiting is enabled.
     # We are receiving the result in KBytes from iperf.
     print("Run guest TX iperf for no rate limiting")
@@ -286,6 +283,8 @@ def _check_rx_rate_limit_patch(test_microvm):
 def _get_tx_bandwidth(test_microvm, host_ip):
     """Check that the rate-limited TX bandwidth is close to what we expect."""
 
+    _start_iperf_server_on_host(test_microvm.netns.cmd_prefix())
+
     iperf_cmd = "{} -c {} -t {} -f KBytes -w {} -N".format(
         IPERF_BINARY, host_ip, IPERF_TRANSMIT_TIME, IPERF_TCP_WINDOW
     )
@@ -350,14 +349,10 @@ def _run_iperf_on_guest(test_microvm, iperf_cmd):
 
 def _start_iperf_server_on_host(netns_cmd_prefix):
     """Start iperf in server mode after killing any leftover iperf daemon."""
-    iperf_cmd = "pkill {}\n".format(IPERF_BINARY)
-
-    # Don't check the result of this command because it can fail if no iperf
-    # is running.
-    utils.run_cmd(iperf_cmd)
+    kill_cmd = f"pkill {IPERF_BINARY}"
+    utils.run_cmd(kill_cmd)
 
     iperf_cmd = "{} {} -sD -f KBytes\n".format(netns_cmd_prefix, IPERF_BINARY)
-
     utils.check_output(iperf_cmd)
 
     # Wait for the iperf daemon to start.