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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