High response time at high concurrent connections

[laltin]

But looking at tornado logs I expect around 2000reqs/sec. Assuming that each
request is handled in 2ms one instance can handle 500reqs/sec and with 4
instances it sholud be 2000req/sec. But it is stuck at 1200reqs/sec I wonder
why it is stuck at that point?
Does increasing the number of instances change the result?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,243246,243255#msg-243255