On Sun, Sep 1, 2013 at 3:16 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I wonder if there is some false sharing going on. But I don't see that
> either, this is the percpu offset map afaik:
>
> 000000000000f560 d files_lglock_lock
> 000000000000f564 d nr_dentry
> 000000000000f568 d last_ino
> 000000000000f56c d nr_unused
> 000000000000f570 d nr_inodes
> 000000000000f574 d vfsmount_lock_lock
> 000000000000f580 d bh_accounting
I made DEFINE_LGLOCK use DEFINE_PER_CPU_SHARED_ALIGNED for the
spinlock, so that each local lock gets its own cacheline, and the
total loops jumped to 62M (from 52-54M before). So when I looked at
the numbers, I thought "oh, that helped".
But then I looked closer, and realized that I just see a fair amount
of boot-to-boot variation anyway (probably a lot to do with cache
placement and how dentries got allocated etc). And it didn't actually
help at all, the problem is stilte there, and lg_local_lock is still
really really high on the profile, at 8% cpu time:
- 8.00% lg_local_lock
- lg_local_lock
+ 64.83% mntput_no_expire
+ 33.81% path_init
+ 0.78% mntput
+ 0.58% path_lookupat
which just looks insane. And no, no lg_global_lock visible anywhere..
So it's not false sharing. But something is bouncing *that* particular
lock around.
Linus
---
34.60% lockref_get_or_lock
23.35% lockref_put_or_lock
10.57% dput
8.00% lg_local_lock
1.79% copy_user_enhanced_fast_string
1.15% link_path_walk
1.04% path_lookupat
1.03% sysret_check
1.01% kmem_cache_alloc
1.00% selinux_inode_permission
0.97% __d_lookup_rcu
0.95% kmem_cache_free
0.90% 0x00007f03e0800ee3
0.88% avc_has_perm_noaudit
0.79% cp_new_stat
0.76% avc_has_perm_flags
0.69% path_init
0.68% getname_flags
0.66% system_call
0.58% generic_permission
0.55% lookup_fast
0.54% user_path_at_empty
0.51% vfs_fstatat
0.49% vfs_getattr
0.49% filename_lookup
0.49% strncpy_from_user
0.44% generic_fillattr
0.40% inode_has_perm.isra.32.constprop.61
0.38% ext4_getattr
0.34% complete_walk
0.34% lg_local_unlock
0.27% d_rcu_to_refcount
0.25% __inode_permission
0.23% _copy_to_user
0.23% security_inode_getattr
0.22% mntget
0.22% selinux_inode_getattr
0.21% SYSC_newstat
0.21% mntput_no_expire
0.20% putname
0.17% path_put
0.16% security_inode_permission
0.16% start_routine
0.14% mntput
0.14% final_putname
0.14% _cond_resched
0.12% inode_permission
0.10% user_path_at
0.09% __xstat64
0.07% sys_newstat
0.03% __xstat@plt
0.03% update_cfs_rq_blocked_load
0.02% task_tick_fair
0.01% common_interrupt
0.01% ktime_get
0.01% lapic_next_deadline
0.01% run_timer_softirq
0.01% hsw_unclaimed_reg_check.isra.6
0.01% sched_clock_cpu
0.01% rcu_check_callbacks
0.01% update_cfs_shares
0.01% _raw_spin_lock
0.01% irqtime_account_irq
0.01% __do_softirq
0.01% ret_from_sys_call
0.01% i915_read32
0.01% hrtimer_interrupt
0.01% update_curr
0.01% profile_tick
0.00% intel_pmu_disable_all
0.00% intel_pmu_enable_all
0.00% tg_load_down
0.00% native_sched_clock
0.00% native_apic_msr_eoi_write
0.00% irqtime_account_process_tick.isra.2
0.00% perf_event_task_tick
0.00% clockevents_program_event
0.00% __acct_update_integrals
0.00% rcu_irq_exit
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