most of value of $request_time is 0.000

[baipeng]

Our version of nginx is nginx/1.0.8 and we have write a third party module to handle the http request. Because the process model of our third party module is synchronous so the nginx worker process will be blocked until one request  accomplished.
The average time cost of one request is about 50ms.But After we set $request_time in nginx.conf, the most of the value of $request_time is 0.000.Even we set timer_resolution 1ms in nginx.conf most of value of $request_time is still 0.000.
Are there anyone can tell me why it occured?
Thx.
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