在nginx / php-fpm配置上同时运行脚本的限制是什么？

The problem is I have to use curl and sometimes the curl requests take a long time because of the timeouts. I have set the timeouts to 1 second so no request should take more than 1 second but still the server is unable to process other php requests.

My question is how many concurrent scripts(running at the same time) can nginx/php-fpm handle. What I see is that a few requests lasting 1 second make the whole server unresponsive. What are the settings that I can change so more requests can be processed at the same time?