正确使用linux inotify - 每次都重启？

Question

我正在调试客户在其生产系统上遇到的系统负载问题,并且他们已经创建了一个模拟负载的测试应用程序来重现问题:

在这个特定的工作量中,编码器所做的一件事就是:

while(1)
  initialize inotify
  watch a directory for events
  receive event
  process event
  remove watch
  close inotify fd

奇怪的是,高系统负载来自close()inotify fd:

inotify_init()                          = 4 <0.000020>
inotify_add_watch(4, "/mnt/tmp/msys_sim/QUEUES/Child_032", IN_CREATE) = 1 <0.059537>
write(1, "Child [032] sleeping\n", 21)  = 21 <0.000012>
read(4, "\1\0\0\0\0\1\0\0\0\0\0\0\20\0\0\0SrcFile.b8tlfT\0\0", 512) = 32 <0.231012>
inotify_rm_watch(4, 1)                  = 0 <0.000044>
close(4)                                = 0 <0.702530>
open("/mnt/tmp/msys_sim/QUEUES/Child_032", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 4 <0.000031>
lseek(4, 0, SEEK_SET)                   = 0 <0.000010>
getdents(4, /* 3 entries */, 32768)     = 88 <0.000048>
getdents(4, /* 0 entries */, 32768)     = 0 <0.000009>
write(1, "Child [032] dequeue [SrcFile.b8t"..., 37) = 37 <0.000011>
unlink("/mnt/tmp/msys_sim/QUEUES/Child_032/SrcFile.b8tlfT") = 0 <0.059298>
lseek(4, 0, SEEK_SET)                   = 0 <0.000011>
getdents(4, /* 2 entries */, 32768)     = 48 <0.000038>
getdents(4, /* 0 entries */, 32768)     = 0 <0.000009>
close(4)                                = 0 <0.000012>
inotify_init()                          = 4 <0.000020>
inotify_add_watch(4, "/mnt/tmp/msys_sim/QUEUES/Child_032", IN_CREATE) = 1 <0.040385>
write(1, "Child [032] sleeping\n", 21)  = 21 <0.000903>
read(4, "\1\0\0\0\0\1\0\0\0\0\0\0\20\0\0\0SrcFile.mQgUSh\0\0", 512) = 32 <0.023423>
inotify_rm_watch(4, 1)                  = 0 <0.000012>
close(4)                                = 0 <0.528736>

什么可能导致close()调用花费如此大量的时间？我可以确定两件事:

• 关闭和重新初始化inotify的每一次
• 有256K文件(平面),/mnt/tmp/msys_sim/SOURCES并且特定文件/mnt/tmp/msys_sim/QUEUES/Child_032硬链接到该目录中的文件.但是SOURCES永远不会被上述过程打开

是使用inotify错误的神器吗？我能指出什么,说"你在做什么是错的!"？

---

输出perf top(我一直在找这个!)

Events: 109K cycles
 70.01%  [kernel]      [k] _spin_lock
 24.30%  [kernel]      [k] __fsnotify_update_child_dentry_flags
  2.24%  [kernel]      [k] _spin_unlock_irqrestore
  0.64%  [kernel]      [k] __do_softirq
  0.60%  [kernel]      [k] __rcu_process_callbacks
  0.46%  [kernel]      [k] run_timer_softirq
  0.40%  [kernel]      [k] rcu_process_gp_end

甜!我怀疑某个地方有一个螺旋锁,当发生这种情况时整个系统会非常潜伏.

Answer 1

通常，伪代码inotify循环如下所示：

initialize inotify
watch a directory | file for events

while(receive event) {
  process event
}

[ remove watch ]
close inotify fd

无需在每个循环中移除手表并重新初始化 inotify。