Messages in this thread | | | Date | Sat, 15 Jun 2013 13:10:17 +0200 | From | Manfred Spraul <> | Subject | Re: [PATCH 0/6] ipc/sem.c: performance improvements, FIFO |
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On 06/14/2013 09:05 PM, Mike Galbraith wrote: > # Events: 802K cycles > # > # Overhead Symbol > # ........ .......................................... > # > 18.42% [k] SYSC_semtimedop > 15.39% [k] sem_lock > 10.26% [k] _raw_spin_lock > 9.00% [k] perform_atomic_semop > 7.89% [k] system_call > 7.70% [k] ipc_obtain_object_check > 6.95% [k] ipcperms > 6.62% [k] copy_user_generic_string > 4.16% [.] __semop > 2.57% [.] worker_thread(void*) > 2.30% [k] copy_from_user > 1.75% [k] sem_unlock > 1.25% [k] ipc_obtain_object ~ 280 mio ops. 2.3% copy_from_user, 9% perform_atomic_semop.
> # Events: 802K cycles > # > # Overhead Symbol > # ........ ............................... > # > 17.38% [k] SYSC_semtimedop > 13.26% [k] system_call > 11.31% [k] copy_user_generic_string > 7.62% [.] __semop > 7.18% [k] _raw_spin_lock > 5.66% [k] ipcperms > 5.40% [k] sem_lock > 4.65% [k] perform_atomic_semop > 4.22% [k] ipc_obtain_object_check > 4.08% [.] worker_thread(void*) > 4.06% [k] copy_from_user > 2.40% [k] ipc_obtain_object > 1.98% [k] pid_vnr > 1.45% [k] wake_up_sem_queue_do > 1.39% [k] sys_semop > 1.35% [k] sys_semtimedop > 1.30% [k] sem_unlock > 1.14% [k] security_ipc_permission ~ 700 mio ops. 4% copy_from_user -> as expected a bit more 4.6% perform_atomic_semop --> less.
Thus: Could you send the oprofile output from perform_atomic_semop()?
Perhaps that gives us a hint.
My current guess: sem_lock() somehow ends up in lock_array. Lock_array scans all struct sem -> transfer of that cacheline from all cpus to the cpu that does the lock_array.. Then the next write by the "correct" cpu causes a transfer back when setting sem->pid.
-- Manfred
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