Understanding behavior of asyncio set_result as it relates to slow_callback_duration

Question

I'm attempting to debug performance of a running production python web service, built on top of tornado using uvloop as the asyncio event loop. In trying to improve the concurrency, I'm looking to find places where synchronous code is being executed that blocks the event loop. To this end, I've configured by service with debug and a slow_callback_duration as such:

    uvloop.install()
    loop = asyncio.get_event_loop()
    loop.set_debug(True)
    loop.slow_callback_duration = 0.05
    server()

With this code enabled, I see a large number of slow callback log lines like the following:

[W 210217 18:12:24.052 asyncio:199] Executing <Handle <TaskWakeupMethWrapper object at 0x7fad2e3cd6a8> created at /usr/local/lib/python3.7/asyncio/tasks.py:711> took 0.105 seconds
[W 210217 18:12:24.164 asyncio:199] Executing <Handle <TaskWakeupMethWrapper object at 0x7fad4d14f768> created at /usr/local/lib/python3.7/asyncio/tasks.py:711> took 0.060 seconds
[W 210217 18:12:24.255 asyncio:199] Executing <Handle <TaskWakeupMethWrapper object at 0x7fad705e2618> created at /usr/local/lib/python3.7/asyncio/tasks.py:711> took 0.083 seconds
[W 210217 18:12:24.387 asyncio:199] Executing <Handle <TaskWakeupMethWrapper object at 0x7fad9b08dd68> created at /usr/local/lib/python3.7/asyncio/tasks.py:711> took 0.077 seconds
[W 210217 18:12:24.682 asyncio:199] Executing <Handle <TaskWakeupMethWrapper object at 0x7fad3716f4c8> created at /usr/local/lib/python3.7/asyncio/tasks.py:711> took 0.058 seconds
[W 210217 18:12:24.899 asyncio:199] Executing <Handle <TaskWakeupMethWrapper object at 0x7fad9b08d528> created at /usr/local/lib/python3.7/asyncio/tasks.py:711> took 0.191 seconds
[W 210217 18:12:24.970 asyncio:199] Executing <Handle <TaskWakeupMethWrapper object at 0x7fad3706ad68> created at /usr/local/lib/python3.7/asyncio/tasks.py:711> took 0.063 seconds
[W 210217 18:12:25.117 asyncio:199] Executing <Handle <TaskWakeupMethWrapper object at 0x7fad2e57c3a8> created at /usr/local/lib/python3.7/asyncio/tasks.py:711> took 0.088 seconds

In my specific python build, that /tasks.py:711 line refers to this call inside the __done__callback of gather:

            if outer._cancel_requested:
                # If gather is being cancelled we must propagate the
                # cancellation regardless of *return_exceptions* argument.
                # See issue 32684.
                outer.set_exception(futures.CancelledError())
            else:
                outer.set_result(results) <--- This line

I'd like to understand better what this debug log line actually represents. From my (limited) understanding of the slow callback behavior it seems like the actual execution of set_result on the wrapping future for gather is taking a long time to execute, but this seems a little bit crazy. Is there a way to get more detail from this debug log and / or determine what code the event loop is actually running when it reports that slow callback?