uwsgi configuration for high traffic

I have a django application and I'm having trouble setting up my server for high traffic. It is very slow with few hits. see my configuration:

[uwsgi]
chdir = /home/meuser/public/meusite.com.br/public_html/
wsgi-file = meusite/wsgi.py
processes = 4
max-requests = 6000
chmod-socket = 666
master = True
vacuum = True
socket = /tmp/uwsgi.sock

Even with varnish and nginx the site is very slow.

How can I resolve this?

I have a vps in the linode of 16GB of RAm, and another of 4gb exclusive to the database.

See settings:

Varnish:

backend default {
    .host = "127.0.0.1";
    .port = "8080";
}


sub vcl_recv
{

# if (req.restarts == 0) {
#       if (req.http.x-forwarded-for) {
#           set req.http.X-Forwarded-For =
#               req.http.X-Forwarded-For + ", " + client.ip;
#       } else {
#           set req.http.X-Forwarded-For = client.ip;
#       }
#     }



  remove req.http.X-Forwarded-For;
  set    req.http.X-Forwarded-For = client.ip;

   # Do not cache example.com, the admin area,
   # logged-in users or POST requests
   if (req.http.host ~ "patoshoje.com.br" ||
        req.url ~ "^/rocha" ||
    req.url ~ "^/admin" ||
        req.http.Cookie ~ "sessionid" ||
        req.request == "POST")
    {
        return (pass);
    }

    # Don't allow cookies to affect cachability
    unset req.http.Cookie;

    # Set Grace Time to one hour
    set req.grace = 1h;
}


sub vcl_fetch
{

    #set bereq.http.X-Real-IP = client.ip;
   # set bereq.http.X-Forwarded-For = req.http.X-Forwarded-For;
    #set bereq.http.host = req.http.host;

    # Set the TTL for cache object to five minutes
    set beresp.ttl = 3m;

    # Set Grace Time to one hour
    set beresp.grace = 1h;

}

Nginx:

upstream mysite {
    server unix:///tmp/uwsgi.sock;
}


server {

    listen 8080;

    server_name www.mysite.com.br mysite.com.br;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;    

    access_log /home/mysite/public/mysite.com.br/log/access.log;
    error_log /home/mysite/public/mysite.com.br/log/error.log;

    root /home/mysite/public/mysite.com.br/public_html;

    charset     utf-8;
    gzip on;
    gzip_disable "msie6";
    gzip_types text/plain text/css application/x-javascript text/xml application/xml application/xml+rss text/javascript;
    gzip_vary on;

    keepalive_timeout 0;
    client_max_body_size 10m;    
    large_client_header_buffers 4 16k;

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
            root   /home/mysite/public/mysite.com.br/public_html/mysite/public/static/;
    }

    location /ckfinder  {
                 alias /home/mysite/public/mysite.com.br/public_html/ckfinder;
                 expires         7d;
                 add_header      pragma public;
                 add_header      cache-control "public";

    }

    location /media  {
                 alias /home/mysite/public/mysite.com.br/public_html/mysite/public/media;
                 expires         7d;
                 add_header      pragma public;
                 add_header      cache-control "public";

    }

    location /static {
         alias /home/mysite/public/mysite.com.br/public_html/mysite/public/static;
         expires         7d;
         add_header      pragma public;
         add_header      cache-control "public";
    }

    location /robots.txt {
        root            /home/mysite/public/mysite.com.br/public_html/mysite/public/static/robots.txt;
        access_log      off;
        log_not_found   off;
    }

   location /favicon.ico {
        root            /home/mysite/public/mysite.com.br/public_html/mysite/public/static/imgs/favicon.png;
        access_log      off;
        log_not_found   off;
   }

   location / {
        uwsgi_pass mysite;
        include     /etc/nginx/uwsgi_params;

   }

}


[uwsgi]
chdir = /home/meuser/public/meusite.com.br/public_html/
wsgi-file = meusite/wsgi.py
processes = 4
max-requests = 6000
chmod-socket = 666
master = True
vacuum = True
socket = /tmp/uwsgi.sock