Nginx slow problem at upstream,need help!

Server NGINX
1

nginx upstream set 2 tomcat links:

upstream tomcats {
server localhost:8080 max_fails=3 fail_timeout=3s;
server localhost:8081 max_fails=3 fail_timeout=3s;

}

server {
listen 80 default;
server_name localhost;

    charset UTF-8;

location / {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://tomcats;

proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
         client_max_body_size 50m;
         client_body_buffer_size 256k;
         proxy_connect_timeout 10;
         proxy_send_timeout 60;
         proxy_read_timeout 60;
         proxy_buffer_size 128k;
         proxy_buffers 8 128k;
         proxy_busy_buffers_size 128k;
         proxy_temp_file_write_size 128k;
proxy_max_temp_file_size 128k;

}
}

at run ab.exe or webbench is slow,but the static html page is very fast.
static html page can run 9000 request/m,but upstream’s 2tomcat is slow.

when i run
ab -n 20000 -c 1000
http://192.168.0.242/CStar/LEAP/CStar/HTML/Login.html

visit has block at:
http://192.168.0.242:80/CStar/LEAP/CStar/HTML/Login.html
visit tomcat is succeed at:
http://192.168.0.242:8081/CStar/LEAP/CStar/HTML/Login.html
or
http://192.168.0.242:8082/CStar/LEAP/CStar/HTML/Login.html

some time visit 1 tomcat has block,but the other one has succeed,always
the nginx is block.

when the ab run end,the nginx some times is block little,some times is
ok.

please help me.

the full config file:

user tomcat tomcat;
worker_processes 2;
#worker_cpu_affinity 00000001 00000010;

error_log /var/log/nginx/error.log notice;

pid /var/run/nginx.pid;

worker_rlimit_nofile 2048;
events {
use epoll;
worker_connections 2048;
}

http {
include mime.types;
default_type application/octet-stream;
source_charset UTF-8;
server_names_hash_bucket_size 256;
client_header_buffer_size 4k;
large_client_header_buffers 4 4k;

#open_file_cache max=65536 inactive=20s;

#size limits
     client_max_body_size             50m;
     client_body_buffer_size        256k;
     client_header_timeout     3m;
     client_body_timeout 3m;
     send_timeout             3m;

#参数都有所调整.目的是解决代理过程中出现的一些502 499错误
sendfile on;
tcp_nopush on;
keepalive_timeout 120; #å‚æ•°åŠ å¤§,以解决做代理时502错误
tcp_nodelay on;

upstream tomcats {
  server localhost:8080 max_fails=3 fail_timeout=3s;
   server localhost:8081 max_fails=3 fail_timeout=3s;

}

server {
    listen       80 default;
    server_name  localhost;

    charset UTF-8;

location / {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://tomcats;

proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
         client_max_body_size 50m;
         client_body_buffer_size 256k;
         proxy_connect_timeout 10;
         proxy_send_timeout 60;
         proxy_read_timeout 60;
         proxy_buffer_size 128k;
         proxy_buffers 8 128k;
         proxy_busy_buffers_size 128k;
         proxy_temp_file_write_size 128k;
proxy_max_temp_file_size 128k;

}
}

server {
    listen       81;
    server_name  localhost;

    charset UTF-8;


    location / {
        root   /f/yumserver;
        index  index.html index.htm;
    }


    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   html;
    }
}

}

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