Profiling Scheduler Performance

When running Dask with TLS security turned on, the scheduler can easily become bottlenecked by SSL communication. See the performance report below, in particular the "Scheduler Profile" tab.

https://gistcdn.githack.com/mrocklin/1d24fbac2c66364d8717952ee8827c64/raw/9c87343cb358b54eb26dbfe8b0714120c0f5ad81/report.html

I ran this on my laptop with the following code

```python
import dask
from dask.distributed import Client, performance_report, wait

client = Client(security=True)

dask.config.set({"optimization.fuse.active": False})

df = dask.datasets.timeseries(start="2020-01-01", end="2020-01-31", partition_freq="1h", freq="60s").persist()

with performance_report("report.html"):
df2 = df.set_index("x").persist()
wait(df2)
```

When this is run on a larger cluster with many workers this problem becomes significantly worse. What are some ways that we can reduce the cost of secure communication?