我正在linux上对nginx + php-fpm进行网络性能测试，env是：
linux ：linux版本2.6.32-358.el6.x86_64（mockbuild@x86-022.build.eng.bos.redhat.com）（gcc版本4.4.7 20120313（Red Hat） 4.4.7-3）（GCC））
nginx ：1.4.6
php ：5.4.26
我继续发送100个并发请求 很长一段时间，然后我看到很多php-fpm日志，如下所示：
[12-Mar-2015 12:16:37] NOTICE: finished trace of 16926
[12-Mar-2015 12:16:37] NOTICE: child 16927 stopped for tracing
[12-Mar-2015 12:16:37] NOTICE: about to trace 16927
[12-Mar-2015 12:16:37] NOTICE: finished trace of 16927
[12-Mar-2015 12:16:37] NOTICE: child 16928 stopped for tracing
[12-Mar-2015 12:16:37] NOTICE: about to trace 16928
[12-Mar-2015 12:16:37] NOTICE: finished trace of 16928
[12-Mar-2015 12:16:37] NOTICE: child 16929 stopped for tracing
[12-Mar-2015 12:16:37] NOTICE: about to trace 16929
[12-Mar-2015 12:16:37] NOTICE: finished trace of 16929
[12-Mar-2015 12:16:37] NOTICE: child 16930 stopped for tracing
[12-Mar-2015 12:16:37] NOTICE: about to trace 16930
[12-Mar-2015 12:16:37] NOTICE: finished trace of 16930
[12-Mar-2015 12:16:37] NOTICE: child 16931 stopped for tracing
[12-Mar-2015 12:16:37] NOTICE: about to trace 16931
[12-Mar-2015 12:16:37] NOTICE: finished trace of 16931
[12-Mar-2015 12:16:37] NOTICE: child 16932 stopped for tracing
[12-Mar-2015 12:16:37] NOTICE: about to trace 16932
[12-Mar-2015 12:16:37] NOTICE: finished trace of 16932
那是什么，这意味着什么？