并发不高，但是一直存在部分请求超时 - Laravel 性能问题?

版本：php 5.6.31 laravel 4.2
并发不高，但是一直存在部分请求超时，有没有大神知道是怎么回事？

[0x00007fc621f39338] hasChildren() /data/www/portal/vendor/symfony/finder/Iterator/ExcludeDirectoryFilterIterator.php:73
[0x00007ffffdd63a80] hasChildren() unknown:0
[0x00007ffffdd63de0] next() unknown:0
[0x00007fc621f391a8] rewind() /data/www/portal/vendor/symfony/finder/Iterator/FilterIterator.php:33
[0x00007ffffdd64200] rewind() unknown:0
[0x00007fc621f38d20] rewind() /data/www/portal/vendor/symfony/finder/Iterator/FilterIterator.php:33
[0x00007ffffdd64620] rewind() unknown:0
[0x00007fc621f38880] gc() /data/www/portal/vendor/laravel/framework/src/Illuminate/Session/FileSessionHandler.php:91
[0x00007fc621f384c8] gc() /data/www/portal/vendor/laravel/framework/src/Illuminate/Session/Middleware.php:159
[0x00007fc621f38280] collectGarbage() /data/www/portal/vendor/laravel/framework/src/Illuminate/Session/Middleware.php:128
[0x00007fc621f380f8] closeSession() /data/www/portal/vendor/laravel/framework/src/Illuminate/Session/Middleware.php:79
[0x00007fc621f37d80] handle() /data/www/portal/vendor/laravel/framework/src/Illuminate/Cookie/Queue.php:47
[0x00007fc621f37aa8] handle() /data/www/portal/vendor/laravel/framework/src/Illuminate/Cookie/Guard.php:51
[0x00007fc621f378d0] handle() /data/www/portal/vendor/stack/builder/src/Stack/StackedHttpKernel.php:23
[0x00007fc621f37758] handle() /data/www/portal/vendor/laravel/framework/src/Illuminate/Foundation/Application.php:641
[0x00007fc621f374c0] run() /data/www/portal/public/index.php:49