We have a twisted application uses the epoll reactor. Sometimes it wastes %100 cpu. It has also some threads for single isolated functions (using deferToThred). First we suspected that threads don't end and goes to an infinite loop. Because application still accepts connections and executes the requested functions. Then I ran the following ps command ps h -Leo pid,pcpu,args,lwp Looking at the output, the main thread seemed to be wasting the whole cpu time. Later on I attached the process to the strace and saw the output below. I don't how does it happen or when does it happen. It is not regular nor repeatable, but this is the strace output when it gets into loop. I send to the list, because it may be useful for someone. Now we switched back to the select reactor. P.S.: We use perspective broker on the server side and qt4reactor for the client. futex(0x8ab6898, FUTEX_WAKE, 1) = 0 epoll_wait(8, {{EPOLLERR|EPOLLHUP, {u32=19, u64=593541665440923667}}}, 8, 15) = 1 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 gettimeofday({1197377318, 796897}, NULL) = 0 gettimeofday({1197377318, 796940}, NULL) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 epoll_wait(8, {{EPOLLERR|EPOLLHUP, {u32=19, u64=593541665440923667}}}, 8, 15) = 1 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 gettimeofday({1197377318, 797127}, NULL) = 0 gettimeofday({1197377318, 797169}, NULL) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 epoll_wait(8, {{EPOLLERR|EPOLLHUP, {u32=19, u64=593541665440923667}}}, 8, 15) = 1 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 gettimeofday({1197377318, 797388}, NULL) = 0 gettimeofday({1197377318, 797430}, NULL) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 epoll_wait(8, {{EPOLLERR|EPOLLHUP, {u32=19, u64=593541665440923667}}}, 8, 14) = 1 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 gettimeofday({1197377318, 797617}, NULL) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 gettimeofday({1197377318, 797692}, NULL) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 epoll_wait(8, {{EPOLLERR|EPOLLHUP, {u32=19, u64=593541665440923667}}}, 8, 14) = 1 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 gettimeofday({1197377318, 797879}, NULL) = 0 gettimeofday({1197377318, 797921}, NULL) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 epoll_wait(8, {{EPOLLERR|EPOLLHUP, {u32=19, u64=593541665440923667}}}, 8, 14) = 1 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 gettimeofday({1197377318, 798139}, NULL) = 0 gettimeofday({1197377318, 798181}, NULL) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 epoll_wait(8, {{EPOLLERR|EPOLLHUP, {u32=19, u64=593541665440923667}}}, 8, 14) = 1 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 gettimeofday({1197377318, 798368}, NULL) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 gettimeofday({1197377318, 798442}, NULL) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 epoll_wait(8, {{EPOLLERR|EPOLLHUP, {u32=19, u64=593541665440923667}}}, 8, 13) = 1 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 gettimeofday({1197377318, 798627}, NULL) = 0 gettimeofday({1197377318, 798669}, NULL) = 0 futex(0x8ab6898, FUTEX_WAKE, 1) = 0 epoll_wait(8, {{EPOLLERR|EPOLLHUP, {u32=19, u64=593541665440923667}}}, 8, 13) = 1 futex(0x8ab6898, FUTEX_WAKE, 1) = 0