Tomcat并发测试报“apr_pollset_create failed: Invalid argument”

Question

测试环境：
Red Hat Enterprise Linux AS release 4 (Nahant Update 6)
Intel(R) Pentium(R) Dual  CPU  E2180  @ 2.00GHz
jdk1.6.0_14
apache-tomcat-6.0.18
apr-1.3.3server.xml配置
<Executor name="tomcatThreadPool" namePrefix="catalina-exec-"
  maxThreads="300" minSpareThreads="100" maxIdleTime="6000"/><Connector port="80" protocol="HTTP/1.1" redirectPort="8443"
               connectionTimeout="20000"
   executor="tomcatThreadPool"
   acceptCount="100"
   enableLookups="false"
   URIEncoding="UTF-8"/>catalina.sh配置
JAVA_OPTS="-Xms512m -Xmx512m"linux下也更改过默认open files值
ulimit -n 8192用ab工具压，并发1024的时候正常。只要超过1024就报apr_pollset_create failed: Invalid argument (22)这样的错
这个是ab进行测试的例子：ab -n 1500 -c 1024 http://172.16.26.128/examples/jsp/jsp2/el/basic-arithmetic.jsp