1 files changed, 139 insertions, 0 deletions

diff --git a/tests/udp_modes.py b/tests/udp_modes.py
new file mode 100644
index 0000000..19cd264
--- /dev/null
+++ b/tests/udp_modes.py
@@ -0,0 +1,139 @@
+"""The four udp arrangements, side by side.
+
+    cc -O2 -pthread -o /tmp/udp_modes tests/udp_modes.c
+    cc -O2 -pthread -o /tmp/udp_load  tests/udp_load.c
+    python3 tests/udp_modes.py
+
+Two questions at once. Down the table: does a shared socket stop scaling as
+threads are added? Across it: does taking several datagrams per syscall make
+that better, or only cheaper?
+
+The receiver does no tracker work by default, so the figure is the kernel's
+receive path and nothing else. WORK_NS=1500 dilutes it back towards what the
+tracker actually costs per announce.
+
+The number reported is cpu microseconds the receiver spent per datagram
+answered, not throughput. Throughput here says more about the load generator
+than the receiver, because both run on the same machine and an echo costs so
+little that the generator runs out of cores first. Cpu per datagram does not
+care: it is what the receive path costs, whoever is the bottleneck.
+"""
+import os
+import signal
+import socket
+import subprocess
+import sys
+import time
+
+MODES = os.environ.get("MODES", "shared per-thread").split()
+BATCHES = [int(n) for n in os.environ.get("BATCHES", "1 8 32").split()]
+THREAD_COUNTS = [int(n) for n in os.environ.get("THREADS", "1 2 4 8").split()]
+LOAD_THREADS = int(os.environ.get("LOAD_THREADS", "4"))
+WINDOW = int(os.environ.get("WINDOW", "32"))
+SECONDS = float(os.environ.get("SECONDS", "3"))
+REPEATS = int(os.environ.get("REPEATS", "2"))
+WORK_NS = int(os.environ.get("WORK_NS", "0"))
+RECEIVER = os.environ.get("UDP_MODES", "/tmp/udp_modes")
+LOADER = os.environ.get("UDP_LOAD", "/tmp/udp_load")
+PORT_BASE = int(os.environ.get("PORT_BASE", "20100"))
+
+
+def cpu_seconds(pid):
+    try:
+        out = subprocess.run(["ps", "-o", "time=", "-p", str(pid)], capture_output=True, text=True).stdout.strip()
+    except OSError:
+        return None
+    if not out:
+        return None
+    total = 0.0
+    for part in out.replace("-", ":").split(":"):
+        total = total * 60 + float(part)
+    return total
+
+
+def one_run(port, threads, mode, batch):
+    receiver = subprocess.Popen(
+        [RECEIVER, str(port), str(threads), mode, str(batch), str(WORK_NS)],
+        stdout=subprocess.DEVNULL, stderr=subprocess.PIPE, text=True,
+    )
+    for _ in range(200):
+        if receiver.poll() is not None:
+            return None, None
+        probe = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+        probe.settimeout(0.1)
+        try:
+            probe.sendto(b"\x00" * 16, ("127.0.0.1", port))
+            probe.recv(64)
+            probe.close()
+            break
+        except OSError:
+            probe.close()
+            time.sleep(0.02)
+    else:
+        receiver.send_signal(signal.SIGINT)
+        receiver.wait()
+        return None, None
+
+    try:
+        subprocess.run([LOADER, "127.0.0.1", str(port), str(LOAD_THREADS), "1", "10000", str(WINDOW)],
+                       stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+        spent, wall = cpu_seconds(receiver.pid), time.time()
+        out = subprocess.run(
+            [LOADER, "127.0.0.1", str(port), str(LOAD_THREADS), str(SECONDS), "10000", str(WINDOW)],
+            capture_output=True, text=True,
+        ).stdout.strip()
+        used = cpu_seconds(receiver.pid)
+    finally:
+        receiver.send_signal(signal.SIGINT)
+        try:
+            receiver.wait(timeout=5)
+        except subprocess.TimeoutExpired:
+            receiver.kill()
+            receiver.wait()
+
+    head = out.split()
+    if not head or not head[0].replace(".", "").isdigit():
+        return None, None
+    cores = (used - spent) / max(time.time() - wall, 1e-9) if (used is not None and spent is not None) else None
+    return float(head[0]), cores
+
+
+def main():
+    for binary in (RECEIVER, LOADER):
+        if not os.path.exists(binary):
+            raise SystemExit("missing %s; see the comment at the top of tests/udp_modes.c" % binary)
+
+    print("  %d load threads x %d in flight, %.0f s x %d runs, %d ns work per datagram"
+          % (LOAD_THREADS, WINDOW, SECONDS, REPEATS, WORK_NS))
+    print("  cpu microseconds per datagram, and the throughput it was measured at")
+    header = "  %-14s %-8s" % ("sockets", "threads")
+    for batch in BATCHES:
+        header += "%20s" % ("%d per syscall" % batch)
+    print(header)
+
+    port = PORT_BASE
+    for mode in MODES:
+        for threads in THREAD_COUNTS:
+            row = "  %-14s %-8d" % (mode, threads)
+            for batch in BATCHES:
+                results = []
+                for _ in range(REPEATS):
+                    port += 1
+                    rate, cores = one_run(port, threads, mode, batch)
+                    if rate:
+                        results.append((rate, cores))
+                if not results:
+                    row += "%18s" % "-"
+                    continue
+                results.sort()
+                rate, cores = results[len(results) // 2]
+                if cores:
+                    row += "%9.2f us %6.0fk/s" % (cores * 1e6 / rate, rate / 1000.0)
+                else:
+                    row += "%20s" % ("%.0fk/s" % (rate / 1000.0))
+            print(row)
+            sys.stdout.flush()
+
+
+if __name__ == "__main__":
+    main()