Tornado comes with limited support for WSGI. However, since WSGI does not support non-blocking requests, you cannot use any of the asynchronous/non-blocking features of Tornado in your application if you choose to use WSGI instead of Tornado's HTTP server. Some of the features that are not available in WSGI applications: @tornado.web.asynchronous, the httpclient module, and the auth module.
in other words: WSGI sucks
EvServer is a lightweight http server, created especially to host python WSGI applications. Additionally, it supports little known Asynchronous WSGI extension, which was suggested by Christopher Stawarz. Using this extension it's possible to create an output html response in many data chunks, without blocking the main server process while your application waits for external resources.
Comet the WSGI way.
On my Apache mod_wsgi setup, I got 235.65 requests per second. That was really good, I thought! However, with the Spawning setup, I got 347.20 requests per second.
another way of deploying WSGI apps with graceful code reloading.