环境：Ubuntu 10.04 LTS、Passenger、Nginx 1.0.6、MySQL、Ruby 1.9.2、Rails 3.1
经过一段时间后，服务器中 CPU 占用率达到 100% 的进程数量逐渐增多
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2393 avitus 20 0 496m 381m 1392 R 100 9.4 25:10.74 Rack: /home/web ...
对任意一个卡住的 PID 运行 strace 都会得到以下结果：
Process 2393 attached with 3 threads - interrupt to quit
[pid 2396] futex(0x8ca80e4, FUTEX_WAIT_PRIVATE, 2, NULL <unfinished ...>
[pid 2394] restart_syscall(<... resuming interrupted call ...>) = -1 ETIMEDOUT (Connection timed out)
[pid 2394] gettimeofday({1322590778, 346573}, NULL) = 0
[pid 2394] futex(0x821db60, FUTEX_WAKE_PRIVATE, 1) = 0
[pid 2394] clock_gettime(CLOCK_REALTIME, {1322590778, 346885177}) = 0
[pid 2394] futex(0x821db84, FUTEX_WAIT_PRIVATE, 33872659, {0, 9687823}) = -1 ETIMEDOUT (Connection timed out)
[pid 2394] gettimeofday({1322590778, 356921}, NULL) = 0
[pid 2394] futex(0x821db60, FUTEX_WAKE_PRIVATE, 1) = 0
[pid 2394] clock_gettime(CLOCK_REALTIME, {1322590778, 357196244}) = 0
[pid 2394] futex(0x821db84, FUTEX_WAIT_PRIVATE, 33872661, {0, 9724756}) = -1 ETIMEDOUT (Connection timed out)
[pid 2394] gettimeofday({1322590778, 367240}, NULL) = 0
[pid 2394] futex(0x821db60, FUTEX_WAKE_PRIVATE, 1) = 0
[pid 2394] clock_gettime(CLOCK_REALTIME, {1322590778, 367459723}) = 0
[pid 2394] futex(0x821db84, FUTEX_WAIT_PRIVATE, 33872663, {0, 9780277}) = -1 ETIMEDOUT (Connection timed out)
[pid 2394] gettimeofday({1322590778, 377586}, NULL) = 0
[pid 2394] futex(0x821db60, FUTEX_WAKE_PRIVATE, 1) = 0
[pid 2394] clock_gettime(CLOCK_REALTIME, {1322590778, 377807840}) = 0
[pid 2394] futex(0x821db84, FUTEX_WAIT_PRIVATE, 33872665, {0, 9778160}) = -1 ETIMEDOUT (Connection timed out)
[pid 2394] gettimeofday({1322590778, 387932}, NULL) = 0
[pid 2394] futex(0x821db60, FUTEX_WAKE_PRIVATE, 1) = 0
[pid 2394] clock_gettime(CLOCK_REALTIME, {1322590778, 388162450}) = 0
[pid 2394] futex(0x821db84, FUTEX_WAIT_PRIVATE, 33872667, {0, 9769550}) = -1 ETIMEDOUT (Connection timed out)
包括 strace 的 'c' 标志将产生：
Process 2393 attached with 3 threads - interrupt to quit
Process 2393 detached Process 2394 detached
Process 2396 detached
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
94.97 0.003172 2 1489 744 futex
3.74 0.000125 0 745 clock_gettime
1.29 0.000043 0 745 gettimeofday
0.00 0.000000 0 1 1 restart_syscall
------ ----------- ----------- --------- --------- ----------------
100.00 0.003340 2980 745 total
我可以用 kill -9 来终止卡住的进程，应用程序和服务器似乎可以顺利运行。我已经想不出如何继续调试了，所以如果有人对原因或其他调查途径有任何建议，我将非常高兴。
答案1
尝试在 Passenger 中将 Passenger_spawn_method 设置为 conservative。我在使用 Mongo 时遇到了这个问题，并遇到了：
http://code.google.com/p/phusion-passenger/issues/detail?id=684
和：
https://github.com/rails/rails/issues/1339
我不知道为什么它不起作用，但如果您还没有找到解决方案的话，希望它能够帮助您。
答案2
这种特殊行为（每 20 毫秒检查一次 futex，然后检查时间）似乎是空闲 Ruby 进程的正常行为：