Do I understand right that at each loop iteration, this client opens a channel to the server and then runs the test case that it has chosen?

Not really. So the main stress_client.php script is run. In each pass to the main loop, it checks whether there is an incoming request from the metrics_client.php script. If there is, respond with the current QPS. If not, choose one interop test case to run. The main stress_client keeps track of how many interop test cases have been run and stop if the deadline is reached.

I meant, specifically, in the case where you're not dealing with the metrics stuff.

When the metrics_client script is run, independently from the stress client, it opens up a connection the metrics server port, and receives the string qps: 201 back in the response, for example. It does not ask for any test case to be run.

I think we've gotten turned around somewhere. I just wanted to point out that every time you run a test case, you open a new channel.

Oh oh, I get it now. Yes, every time the stress test client runs an interop test, a channel got created (to the interop server, yes). It ties into issue #6231 where currently we don't have a way to re-use a channel.

The Node stress client reuses the stub.

Now I am re-using the interop client stub. PTAL, thanks!

One of the sanity tests failing:

copyright missing: src/php/tests/interop/metrics_client.php
copyright missing: src/php/tests/interop/stress_client.php

Other than the above, everything else LGTM

Fixed copyright.

PHP tests are green

Yes, LGTM. Can be merged.