oneshot performance?

[cavemanloverboy]

Why exactly is there an almost 100x difference in performance in the runtimes for the sync_mpsc_oneshot bench? seems quite unacceptable

test request_reply_current_thread ... bench:     339,371 ns/iter (+/- 6,729)
test request_reply_multi_threaded ... bench:  18,261,453 ns/iter (+/- 15,988,765)

[wathenjiang]

It is because that although we set the number of worker threads of request_reply_multi_threaded to 1, the async task scheduler behind the tokio runtime is different from the request_reply_current_thread.

To be specific, in the request_reply_current_thread, we only use the main thread which is the thread run the fn main for scheduling async Task, so there are no multi-threaded concurrent read and write. But in the request_reply_multi_threaded, there are main thread and only one worker thread. The main thread take care of task_tx.send(o_tx).await.unwrap(); and the worker thread take care of the code in the tokio::spawn. There are multi-threaded concurrent read and write between main thread and the only one worker thread.

In such case, multithreading will cause the worse performance, as the above benchmark says.