Re: question about RCU dynticks_nesting

[Mike Galbraith <umgwanakikbuti@gmail.com>]

On Wed, 2015-05-06 at 03:49 +0200, Mike Galbraith wrote:
> On Mon, 2015-05-04 at 22:54 -0700, Paul E. McKenney wrote:
> 
> > You have RCU_FAST_NO_HZ=y, correct?  Could you please try measuring with
> > RCU_FAST_NO_HZ=n?
> 
> FWIW, the syscall numbers I posted were RCU_FAST_NO_HZ=n.  (I didn't
> profile to see where costs lie though)

(did that)

100000000 * stat() on isolated cpu

NO_HZ_FULL off        inactive     housekeeper    nohz_full
real    0m14.266s     0m14.367s    0m20.427s      0m27.921s 
user    0m1.756s      0m1.553s     0m1.976s       0m10.447s
sys     0m12.508s     0m12.769s    0m18.400s      0m17.464s
(real)  1.000         1.007        1.431          1.957

 inactive                                         housekeeper                                        nohz_full
----------------------------------------------------------------------------------------------------------------------------------------------
 7.61%  [.] __xstat64                             11.12%  [k] context_tracking_exit                  7.41%  [k] context_tracking_exit
 7.04%  [k] system_call                            6.18%  [k] context_tracking_enter                 6.02%  [k] native_sched_clock
 6.96%  [k] copy_user_enhanced_fast_string         5.18%  [.] __xstat64                              4.69%  [k] rcu_eqs_enter_common.isra.37
 6.57%  [k] path_init                              4.89%  [k] system_call                            4.35%  [k] _raw_spin_lock
 5.92%  [k] system_call_after_swapgs               4.84%  [k] copy_user_enhanced_fast_string         4.30%  [k] context_tracking_enter
 5.44%  [k] lockref_put_return                     4.46%  [k] path_init                              4.25%  [k] kmem_cache_alloc
 4.69%  [k] link_path_walk                         4.30%  [k] system_call_after_swapgs               4.14%  [.] __xstat64
 4.47%  [k] lockref_get_not_dead                   4.12%  [k] kmem_cache_free                        3.89%  [k] rcu_eqs_exit_common.isra.38
 4.46%  [k] kmem_cache_free                        3.78%  [k] link_path_walk                         3.50%  [k] system_call
 4.20%  [k] kmem_cache_alloc                       3.62%  [k] lockref_put_return                     3.48%  [k] copy_user_enhanced_fast_string
 4.09%  [k] cp_new_stat                            3.43%  [k] kmem_cache_alloc                       3.02%  [k] system_call_after_swapgs
 3.38%  [k] vfs_getattr_nosec                      2.95%  [k] lockref_get_not_dead                   2.97%  [k] kmem_cache_free
 2.82%  [k] vfs_fstatat                            2.87%  [k] cp_new_stat                            2.88%  [k] lockref_put_return
 2.60%  [k] user_path_at_empty                     2.62%  [k] syscall_trace_leave                    2.61%  [k] link_path_walk
 2.47%  [k] path_lookupat                          1.91%  [k] vfs_getattr_nosec                      2.58%  [k] path_init
 2.14%  [k] strncpy_from_user                      1.89%  [k] syscall_trace_enter_phase1             2.15%  [k] lockref_get_not_dead
 2.11%  [k] getname_flags                          1.77%  [k] path_lookupat                          2.04%  [k] cp_new_stat
 2.10%  [k] generic_fillattr                       1.67%  [k] complete_walk                          1.89%  [k] generic_fillattr
 2.05%  [.] main                                   1.65%  [k] vfs_fstatat                            1.67%  [k] syscall_trace_leave
 1.89%  [k] complete_walk                          1.56%  [k] generic_fillattr                       1.59%  [k] vfs_getattr_nosec
 1.73%  [k] generic_permission                     1.55%  [k] user_path_at_empty                     1.49%  [k] get_vtime_delta
 1.50%  [k] system_call_fastpath                   1.54%  [k] strncpy_from_user                      1.32%  [k] user_path_at_empty
 1.37%  [k] legitimize_mnt                         1.53%  [k] getname_flags                          1.30%  [k] syscall_trace_enter_phase1
 1.30%  [k] dput                                   1.46%  [k] legitimize_mnt                         1.21%  [k] rcu_eqs_exit
 1.26%  [k] putname                                1.34%  [.] main                                   1.21%  [k] vfs_fstatat
 1.19%  [k] path_put                               1.32%  [k] int_with_check                         1.18%  [k] path_lookupat
 1.18%  [k] filename_lookup                        1.28%  [k] generic_permission                     1.15%  [k] getname_flags
 1.01%  [k] SYSC_newstat                           1.16%  [k] int_very_careful                       1.03%  [k] strncpy_from_user
 0.96%  [k] mntput_no_expire                       1.04%  [k] putname                                1.01%  [k] account_system_time
 0.79%  [k] path_cleanup                           0.94%  [k] dput                                   1.00%  [k] complete_walk
 0.79%  [k] mntput                                 0.91%  [k] context_tracking_user_exit             0.99%  [k] vtime_account_user