test_load.py

import asyncio
import time
import random


async def coro(loop, idx):
    # distribute coros homogenity along 10 seconds
    # to get a homogeneous traffic.
    await asyncio.sleep(idx % 10)
    if loop.load() > 0.9:
        return False
    start = loop.time()
    while loop.time() - start < 0.02:
        pass
    return True

async def run(loop, n):
    tasks = [coro(loop, i) for i in range(n)]
    results = await asyncio.gather(*tasks)
    abandoned = len([r for r in results if not r])
    print("Load reached for {} coros/seq: {}, abandoned {}/{}".format(n/10, loop.load(), abandoned, n))

async def wait_load_zero():
    print("reseting load....")
    await asyncio.sleep(6)

async def main(loop):
    await run(loop, 100)
    await wait_load_zero()
    await run(loop, 200)
    await wait_load_zero()
    await run(loop, 400)
    await wait_load_zero()
    await run(loop, 800)

loop = asyncio.get_event_loop()
loop.run_until_complete(main(loop))

$ ./python.exe ../test_load2.py
Load reached for 10.0 coros/seq: 0.20594804872227002, abandoned 0/100
reseting load....
Load reached for 20.0 coros/seq: 0.40599215789994814, abandoned 0/200
reseting load....
Load reached for 40.0 coros/seq: 0.8055964270483202, abandoned 0/400
reseting load....
Load reached for 80.0 coros/seq: 0.9390106831339007, abandoned 450/800