So there is no keep alive in these tests including lb to application? Makes sense why the qps is so low on a single core for all versions tested if nginx is having to reopening a new socket each time to zerohttpd. Not sure how useful this is as keeping your connection alive to your lb is important for throughput.
Not in all use-cases. If your backend is serving long-lived HTTP streams (big downloads; chunked SSE streams; websocket sessions), it may make more sense to close and re-open those sockets between sessions, since they live long enough to establish TCP window characteristics that may not apply to the session succeeding them (e.g. an interactive-RPC websocket session, reusing a TCP connection previously used to stream a GB of data using huge packets, will start off quite a bit slower for its use-case than a “fresh” TCP session would.)
Keep-alive is a win in most situations, but especially so in any kind of benchmarking, since it's very easy to hit bottlenecks in opening/accepting new connections, e.g. running out of ports. If you are opening and closing thousands of connections, port space / TCP tuning can become the limiting factor, regardless of your server architecture.
