Re: [patch 00/16] CFS Bandwidth Control v7
From: Hu Tao
Date: Mon Jul 04 2011 - 23:58:54 EST
On Fri, Jul 01, 2011 at 02:28:24PM +0200, Ingo Molnar wrote:
>
> * Hu Tao <hutao@xxxxxxxxxxxxxx> wrote:
>
> > > Yeah, these numbers look pretty good. Note that the percentages
> > > in the third column (the amount of time that particular event was
> > > measured) is pretty low, and it would be nice to eliminate it:
> > > i.e. now that we know the ballpark figures do very precise
> > > measurements that do not over-commit the PMU.
> > >
> > > One such measurement would be:
> > >
> > > -e cycles -e instructions -e branches
> > >
> > > This should also bring the stddev percentages down i think, to
> > > below 0.1%.
> > >
> > > Another measurement would be to test not just the feature-enabled
> > > but also the feature-disabled cost - so that we document the
> > > rough overhead that users of this new scheduler feature should
> > > expect.
> > >
> > > Organizing it into neat before/after numbers and percentages,
> > > comparing it with noise (stddev) [i.e. determining that the
> > > effect we measure is above noise] and putting it all into the
> > > changelog would be the other goal of these measurements.
> >
> > Hi Ingo,
> >
> > I've tested pipe-test-100k in the following cases: base(no patch),
> > with patch but feature-disabled, with patch and several
> > periods(quota set to be a large value to avoid processes
> > throttled), the result is:
> >
> >
> > cycles instructions branches
> > -------------------------------------------------------------------------------------------------------------------
> > base 7,526,317,497 8,666,579,347 1,771,078,445
> > +patch, cgroup not enabled 7,610,354,447 (1.12%) 8,569,448,982 (-1.12%) 1,751,675,193 (-0.11%)
> > +patch, 10000000000/1000(quota/period) 7,856,873,327 (4.39%) 8,822,227,540 (1.80%) 1,801,766,182 (1.73%)
> > +patch, 10000000000/10000(quota/period) 7,797,711,600 (3.61%) 8,754,747,746 (1.02%) 1,788,316,969 (0.97%)
> > +patch, 10000000000/100000(quota/period) 7,777,784,384 (3.34%) 8,744,979,688 (0.90%) 1,786,319,566 (0.86%)
> > +patch, 10000000000/1000000(quota/period) 7,802,382,802 (3.67%) 8,755,638,235 (1.03%) 1,788,601,070 (0.99%)
> > -------------------------------------------------------------------------------------------------------------------
>
> ok, i had a quick look at the stddev numbers as well and most seem
> below the 0.1 range, well below the effects you managed to measure.
> So i think this table is pretty accurate and we can rely on it for
> analysis.
>
> So we've got a +1.1% incrase in overhead with cgroups disabled, while
> the instruction count went down by 1.1%. Is this expected? If you
> profile stalled cycles and use perf diff between base and patched
> kernels, does it show you some new hotspot that causes the overhead?
perf diff shows 0.43% increase in sched_clock, and 0.98% decrease in
pipe_unlock. the complete output is attached.
>
> To better understand the reasons behind that result, could you try to
> see whether the cycles count is stable across reboots as well, or
> does it vary beyond the ~1% value that you measure?
>
> One thing that can help validating the measurements is to do:
>
> echo 1 > /proc/sys/vm/drop_caches
>
> Before testing. This helps re-establish the whole pagecache layout
> (which gives a lot of the across-boot variability of such
> measurements).
I have tested three times for base and +patch,cgroup not enabled
repectively (each time reboot, drop_caches then perf). the data
seems stable comparing to those in the table above, see below:
cycles instructions
------------------------------------------------------------------
base 7,526,317,497 8,666,579,347
base, drop_caches 7,518,958,711 (-0.10%) 8,634,136,901(-0.37%)
base, drop_caches 7,526,419,287 (+0.00%) 8,641,162,766(-0.29%)
base, drop_caches 7,491,864,402 (-0.46%) 8,624,760,925(-0.48%)
cycles instructions
--------------------------------------------------------------------------------------
+patch, cgroup disabled 7,610,354,447 8,569,448,982
+patch, cgroup disabled, drop_caches 7,574,623,093 (-0.47%) 8,572,061,001 (+0.03%)
+patch, cgroup disabled, drop_caches 7,594,083,776 (-0.21%) 8,574,447,382 (+0.06%)
+patch, cgroup disabled, drop_caches 7,584,913,316 (-0.33%) 8,574,734,269 (+0.06%)
perf diff output:
# Baseline Delta Shared Object Symbol
# ........ .......... ................. ...........................
#
0.00% +10.07% [kernel.kallsyms] [k] __lock_acquire
0.00% +5.90% [kernel.kallsyms] [k] lock_release
0.00% +4.86% [kernel.kallsyms] [k] trace_hardirqs_off_caller
0.00% +4.06% [kernel.kallsyms] [k] debug_smp_processor_id
0.00% +4.00% [kernel.kallsyms] [k] lock_acquire
0.00% +3.81% [kernel.kallsyms] [k] lock_acquired
0.00% +3.71% [kernel.kallsyms] [k] lock_is_held
0.00% +3.04% [kernel.kallsyms] [k] validate_chain
0.00% +2.68% [kernel.kallsyms] [k] check_chain_key
0.00% +2.41% [kernel.kallsyms] [k] trace_hardirqs_off
0.00% +2.01% [kernel.kallsyms] [k] trace_hardirqs_on_caller
2.04% -0.09% pipe-test-100k [.] main
0.00% +1.79% [kernel.kallsyms] [k] add_preempt_count
0.00% +1.67% [kernel.kallsyms] [k] lock_release_holdtime
0.00% +1.67% [kernel.kallsyms] [k] mutex_lock_nested
0.00% +1.61% [kernel.kallsyms] [k] pipe_read
0.00% +1.58% [kernel.kallsyms] [k] local_clock
1.13% +0.43% [kernel.kallsyms] [k] sched_clock
0.00% +1.52% [kernel.kallsyms] [k] sub_preempt_count
0.00% +1.39% [kernel.kallsyms] [k] _raw_spin_unlock_irqrestore
1.14% +0.15% libc-2.12.so [.] __GI___libc_read
0.00% +1.21% [kernel.kallsyms] [k] mark_lock
0.00% +1.06% [kernel.kallsyms] [k] __mutex_unlock_slowpath
0.00% +1.03% [kernel.kallsyms] [k] match_held_lock
0.00% +0.96% [kernel.kallsyms] [k] copy_user_generic_string
0.00% +0.93% [kernel.kallsyms] [k] schedule
0.00% +0.76% [kernel.kallsyms] [k] __list_del_entry
0.00% +0.73% [kernel.kallsyms] [k] enqueue_entity
0.00% +0.68% [kernel.kallsyms] [k] cpuacct_charge
0.00% +0.62% [kernel.kallsyms] [k] trace_preempt_off
0.00% +0.59% [kernel.kallsyms] [k] vfs_write
0.00% +0.56% [kernel.kallsyms] [k] trace_preempt_on
0.00% +0.56% [kernel.kallsyms] [k] system_call
0.00% +0.55% [kernel.kallsyms] [k] sys_read
0.00% +0.54% [kernel.kallsyms] [k] pipe_write
0.00% +0.53% [kernel.kallsyms] [k] get_parent_ip
0.00% +0.53% [kernel.kallsyms] [k] vfs_read
0.00% +0.53% [kernel.kallsyms] [k] put_lock_stats
0.56% -0.03% [kernel.kallsyms] [k] intel_pmu_enable_all
0.00% +0.51% [kernel.kallsyms] [k] fsnotify
0.72% -0.23% libc-2.12.so [.] __GI___libc_write
0.00% +0.49% [kernel.kallsyms] [k] do_sync_write
0.00% +0.48% [kernel.kallsyms] [k] trace_hardirqs_on
0.00% +0.48% [kernel.kallsyms] [k] do_sync_read
0.00% +0.45% [kernel.kallsyms] [k] dequeue_entity
0.00% +0.44% [kernel.kallsyms] [k] select_task_rq_fair
0.00% +0.44% [kernel.kallsyms] [k] update_curr
0.00% +0.43% [kernel.kallsyms] [k] fget_light
0.00% +0.42% [kernel.kallsyms] [k] do_raw_spin_trylock
0.00% +0.42% [kernel.kallsyms] [k] in_lock_functions
0.00% +0.40% [kernel.kallsyms] [k] find_next_bit
0.50% -0.11% [kernel.kallsyms] [k] intel_pmu_disable_all
0.00% +0.39% [kernel.kallsyms] [k] __list_add
0.00% +0.38% [kernel.kallsyms] [k] enqueue_task
0.00% +0.38% [kernel.kallsyms] [k] __might_sleep
0.00% +0.38% [kernel.kallsyms] [k] kill_fasync
0.00% +0.36% [kernel.kallsyms] [k] check_flags
0.00% +0.36% [kernel.kallsyms] [k] _raw_spin_unlock
0.00% +0.34% [kernel.kallsyms] [k] pipe_iov_copy_from_user
0.00% +0.33% [kernel.kallsyms] [k] check_preempt_curr
0.00% +0.32% [kernel.kallsyms] [k] system_call_after_swapgs
0.00% +0.32% [kernel.kallsyms] [k] mark_held_locks
0.00% +0.31% [kernel.kallsyms] [k] touch_atime
0.00% +0.30% [kernel.kallsyms] [k] account_entity_enqueue
0.00% +0.30% [kernel.kallsyms] [k] set_next_entity
0.00% +0.30% [kernel.kallsyms] [k] place_entity
0.00% +0.29% [kernel.kallsyms] [k] try_to_wake_up
0.00% +0.29% [kernel.kallsyms] [k] check_preempt_wakeup
0.00% +0.28% [kernel.kallsyms] [k] debug_lockdep_rcu_enabled
0.00% +0.28% [kernel.kallsyms] [k] cpumask_next_and
0.00% +0.28% [kernel.kallsyms] [k] __wake_up_common
0.00% +0.27% [kernel.kallsyms] [k] rb_erase
0.00% +0.26% [kernel.kallsyms] [k] ttwu_stat
0.00% +0.25% [kernel.kallsyms] [k] _raw_spin_unlock_irq
0.00% +0.25% [kernel.kallsyms] [k] pick_next_task_fair
0.00% +0.25% [kernel.kallsyms] [k] update_cfs_shares
0.00% +0.25% [kernel.kallsyms] [k] sysret_check
0.00% +0.25% [kernel.kallsyms] [k] lockdep_sys_exit_thunk
0.00% +0.25% [kernel.kallsyms] [k] _raw_spin_lock_irqsave
0.00% +0.24% [kernel.kallsyms] [k] get_lock_stats
0.00% +0.24% [kernel.kallsyms] [k] put_prev_task_fair
0.00% +0.24% [kernel.kallsyms] [k] trace_hardirqs_on_thunk
0.00% +0.24% [kernel.kallsyms] [k] __perf_event_task_sched_out
0.00% +0.24% [kernel.kallsyms] [k] ret_from_sys_call
0.00% +0.23% [kernel.kallsyms] [k] rcu_note_context_switch
0.00% +0.23% [kernel.kallsyms] [k] update_stats_wait_end
0.00% +0.23% [kernel.kallsyms] [k] file_update_time
0.35% -0.12% libc-2.12.so [.] __write_nocancel
0.00% +0.22% [kernel.kallsyms] [k] rw_verify_area
0.00% +0.21% [kernel.kallsyms] [k] mutex_unlock
0.00% +0.20% [kernel.kallsyms] [k] system_call_fastpath
0.00% +0.20% [kernel.kallsyms] [k] sys_write
0.09% +0.11% [kernel.kallsyms] [k] update_cfs_load
0.00% +0.20% [kernel.kallsyms] [k] time_hardirqs_off
0.10% +0.10% [kernel.kallsyms] [k] x86_pmu_disable
0.00% +0.19% [kernel.kallsyms] [k] clear_buddies
0.00% +0.19% [kernel.kallsyms] [k] activate_task
0.00% +0.18% [kernel.kallsyms] [k] enqueue_task_fair
0.00% +0.18% [kernel.kallsyms] [k] _raw_spin_lock
0.00% +0.18% [kernel.kallsyms] [k] ttwu_do_wakeup
0.00% +0.17% [kernel.kallsyms] [k] __srcu_read_lock
0.00% +0.17% [kernel.kallsyms] [k] prepare_to_wait
0.00% +0.16% [kernel.kallsyms] [k] debug_mutex_lock_common
0.00% +0.16% [kernel.kallsyms] [k] ttwu_activate
0.00% +0.16% [kernel.kallsyms] [k] time_hardirqs_on
0.00% +0.16% [kernel.kallsyms] [k] pipe_wait
0.00% +0.16% [kernel.kallsyms] [k] preempt_schedule
0.00% +0.16% [kernel.kallsyms] [k] debug_mutex_free_waiter
0.00% +0.15% [kernel.kallsyms] [k] __rcu_read_unlock
0.00% +0.14% [kernel.kallsyms] [k] account_cfs_rq_runtime
0.00% +0.14% [kernel.kallsyms] [k] perf_pmu_rotate_start
0.00% +0.14% [kernel.kallsyms] [k] pipe_lock
0.00% +0.14% [kernel.kallsyms] [k] __perf_event_task_sched_in
0.00% +0.14% [kernel.kallsyms] [k] __srcu_read_unlock
0.00% +0.13% [kernel.kallsyms] [k] perf_ctx_unlock
0.00% +0.13% [kernel.kallsyms] [k] __rcu_read_lock
0.00% +0.13% [kernel.kallsyms] [k] account_entity_dequeue
0.00% +0.12% [kernel.kallsyms] [k] __fsnotify_parent
0.00% +0.12% [kernel.kallsyms] [k] sched_clock_cpu
0.00% +0.12% [kernel.kallsyms] [k] current_fs_time
0.00% +0.11% [kernel.kallsyms] [k] _raw_spin_lock_irq
0.00% +0.11% [kernel.kallsyms] [k] mutex_remove_waiter
0.00% +0.11% [kernel.kallsyms] [k] autoremove_wake_function
0.00% +0.10% [kernel.kallsyms] [k] hrtick_start_fair
0.08% +0.03% pipe-test-100k [.] read@plt
0.00% +0.10% [kernel.kallsyms] [k] __bfs
0.00% +0.10% [kernel.kallsyms] [k] mnt_want_write
0.00% +0.09% [kernel.kallsyms] [k] __dequeue_entity
0.00% +0.09% [kernel.kallsyms] [k] do_raw_spin_unlock
0.00% +0.08% [kernel.kallsyms] [k] lockdep_sys_exit
0.00% +0.08% [kernel.kallsyms] [k] rb_next
0.00% +0.08% [kernel.kallsyms] [k] debug_mutex_unlock
0.00% +0.08% [kernel.kallsyms] [k] rb_insert_color
0.00% +0.08% [kernel.kallsyms] [k] update_rq_clock
0.00% +0.08% [kernel.kallsyms] [k] dequeue_task_fair
0.00% +0.07% [kernel.kallsyms] [k] finish_wait
0.00% +0.07% [kernel.kallsyms] [k] wakeup_preempt_entity
0.00% +0.07% [kernel.kallsyms] [k] debug_mutex_add_waiter
0.00% +0.07% [kernel.kallsyms] [k] ttwu_do_activate.clone.3
0.00% +0.07% [kernel.kallsyms] [k] generic_pipe_buf_map
0.00% +0.06% [kernel.kallsyms] [k] __wake_up_sync_key
0.00% +0.06% [kernel.kallsyms] [k] __mark_inode_dirty
0.04% +0.02% [kernel.kallsyms] [k] intel_pmu_nhm_enable_all
0.00% +0.05% [kernel.kallsyms] [k] timespec_trunc
0.00% +0.05% [kernel.kallsyms] [k] dequeue_task
0.00% +0.05% [kernel.kallsyms] [k] perf_pmu_disable
0.00% +0.05% [kernel.kallsyms] [k] apic_timer_interrupt
0.00% +0.05% [kernel.kallsyms] [k] current_kernel_time
0.05% pipe-test-100k [.] write@plt
0.00% +0.05% [kernel.kallsyms] [k] generic_pipe_buf_confirm
0.00% +0.04% [kernel.kallsyms] [k] __rcu_pending
0.00% +0.04% [kernel.kallsyms] [k] generic_pipe_buf_unmap
0.00% +0.04% [kernel.kallsyms] [k] anon_pipe_buf_release
0.00% +0.04% [kernel.kallsyms] [k] finish_task_switch
0.00% +0.04% [kernel.kallsyms] [k] perf_event_context_sched_in
0.00% +0.04% [kernel.kallsyms] [k] update_process_times
0.00% +0.04% [kernel.kallsyms] [k] do_timer
0.00% +0.04% [kernel.kallsyms] [k] trace_hardirqs_off_thunk
0.00% +0.03% [kernel.kallsyms] [k] run_timer_softirq
0.00% +0.02% [kernel.kallsyms] [k] default_wake_function
0.00% +0.02% [kernel.kallsyms] [k] hrtimer_interrupt
0.00% +0.02% [kernel.kallsyms] [k] timerqueue_add
0.00% +0.02% [kernel.kallsyms] [k] __do_softirq
0.00% +0.02% [kernel.kallsyms] [k] set_next_buddy
0.00% +0.02% [kernel.kallsyms] [k] resched_task
0.00% +0.02% [kernel.kallsyms] [k] task_tick_fair
0.00% +0.02% [kernel.kallsyms] [k] restore
0.00% +0.02% [kernel.kallsyms] [k] irq_exit
0.00% +0.02% [e1000e] [k] e1000_watchdog
0.00% +0.01% [kernel.kallsyms] [k] account_process_tick
0.00% +0.01% [kernel.kallsyms] [k] update_vsyscall
0.00% +0.01% [kernel.kallsyms] [k] rcu_enter_nohz
0.00% +0.01% [kernel.kallsyms] [k] hrtimer_run_pending
0.00% +0.01% [kernel.kallsyms] [k] calc_global_load
0.00% +0.01% [kernel.kallsyms] [k] account_system_time
0.00% +0.01% [kernel.kallsyms] [k] __run_hrtimer
0.99% -0.98% [kernel.kallsyms] [k] pipe_unlock
0.00% +0.01% [kernel.kallsyms] [k] irq_enter
0.00% +0.01% [kernel.kallsyms] [k] scheduler_tick
0.00% +0.01% [kernel.kallsyms] [k] mnt_want_write_file
0.00% +0.01% [kernel.kallsyms] [k] hrtimer_run_queues
0.01% [kernel.kallsyms] [k] sched_avg_update
0.00% [kernel.kallsyms] [k] rcu_check_callbacks
0.00% [kernel.kallsyms] [k] task_waking_fair
0.00% [kernel.kallsyms] [k] trace_softirqs_off
0.00% [kernel.kallsyms] [k] call_softirq
0.00% [kernel.kallsyms] [k] find_busiest_group
0.00% [kernel.kallsyms] [k] exit_idle
0.00% [kernel.kallsyms] [k] enqueue_hrtimer
0.00% [kernel.kallsyms] [k] hrtimer_forward
0.02% -0.02% [kernel.kallsyms] [k] x86_pmu_enable
0.01% [kernel.kallsyms] [k] do_softirq
0.00% [kernel.kallsyms] [k] calc_delta_mine
0.00% [kernel.kallsyms] [k] sched_slice
0.00% [kernel.kallsyms] [k] tick_sched_timer
0.00% [kernel.kallsyms] [k] irq_work_run
0.00% [kernel.kallsyms] [k] ktime_get
0.00% [kernel.kallsyms] [k] update_cpu_load
0.00% [kernel.kallsyms] [k] __remove_hrtimer
0.00% [kernel.kallsyms] [k] rcu_exit_nohz
0.00% [kernel.kallsyms] [k] clockevents_program_event
and perf stat outputs:
base, drop_caches:
Performance counter stats for './pipe-test-100k' (50 runs):
3841.033842 task-clock # 0.576 CPUs utilized ( +- 0.06% )
200,008 context-switches # 0.052 M/sec ( +- 0.00% )
0 CPU-migrations # 0.000 M/sec ( +- 56.54% )
135 page-faults # 0.000 M/sec ( +- 0.16% )
7,518,958,711 cycles # 1.958 GHz ( +- 0.09% )
2,676,161,995 stalled-cycles-frontend # 35.59% frontend cycles idle ( +- 0.17% )
1,152,912,513 stalled-cycles-backend # 15.33% backend cycles idle ( +- 0.31% )
8,634,136,901 instructions # 1.15 insns per cycle
# 0.31 stalled cycles per insn ( +- 0.08% )
1,764,912,243 branches # 459.489 M/sec ( +- 0.08% )
35,531,303 branch-misses # 2.01% of all branches ( +- 0.12% )
6.669821483 seconds time elapsed ( +- 0.03% )
base, drop_caches:
Performance counter stats for './pipe-test-100k' (50 runs):
3840.203514 task-clock # 0.576 CPUs utilized ( +- 0.06% )
200,009 context-switches # 0.052 M/sec ( +- 0.00% )
0 CPU-migrations # 0.000 M/sec ( +- 60.19% )
135 page-faults # 0.000 M/sec ( +- 0.18% )
7,526,419,287 cycles # 1.960 GHz ( +- 0.08% )
2,681,342,567 stalled-cycles-frontend # 35.63% frontend cycles idle ( +- 0.15% )
1,159,603,323 stalled-cycles-backend # 15.41% backend cycles idle ( +- 0.36% )
8,641,162,766 instructions # 1.15 insns per cycle
# 0.31 stalled cycles per insn ( +- 0.07% )
1,766,192,649 branches # 459.922 M/sec ( +- 0.07% )
35,520,560 branch-misses # 2.01% of all branches ( +- 0.11% )
6.667852851 seconds time elapsed ( +- 0.03% )
base, drop_caches:
Performance counter stats for './pipe-test-100k' (50 runs):
3827.952520 task-clock # 0.575 CPUs utilized ( +- 0.06% )
200,009 context-switches # 0.052 M/sec ( +- 0.00% )
0 CPU-migrations # 0.000 M/sec ( +- 56.54% )
135 page-faults # 0.000 M/sec ( +- 0.17% )
7,491,864,402 cycles # 1.957 GHz ( +- 0.08% )
2,664,949,808 stalled-cycles-frontend # 35.57% frontend cycles idle ( +- 0.16% )
1,140,326,742 stalled-cycles-backend # 15.22% backend cycles idle ( +- 0.31% )
8,624,760,925 instructions # 1.15 insns per cycle
# 0.31 stalled cycles per insn ( +- 0.07% )
1,761,666,011 branches # 460.211 M/sec ( +- 0.07% )
34,655,390 branch-misses # 1.97% of all branches ( +- 0.12% )
6.657224884 seconds time elapsed ( +- 0.03% )
+patch, cgroup disabled, drop_caches:
Performance counter stats for './pipe-test-100k' (50 runs):
3857.191852 task-clock # 0.576 CPUs utilized ( +- 0.09% )
200,008 context-switches # 0.052 M/sec ( +- 0.00% )
0 CPU-migrations # 0.000 M/sec ( +- 42.86% )
135 page-faults # 0.000 M/sec ( +- 0.19% )
7,574,623,093 cycles # 1.964 GHz ( +- 0.10% )
2,758,696,094 stalled-cycles-frontend # 36.42% frontend cycles idle ( +- 0.15% )
1,239,909,382 stalled-cycles-backend # 16.37% backend cycles idle ( +- 0.38% )
8,572,061,001 instructions # 1.13 insns per cycle
# 0.32 stalled cycles per insn ( +- 0.08% )
1,750,572,714 branches # 453.846 M/sec ( +- 0.08% )
36,051,335 branch-misses # 2.06% of all branches ( +- 0.13% )
6.691634724 seconds time elapsed ( +- 0.04% )
+patch, cgroup disabled, drop_caches:
Performance counter stats for './pipe-test-100k' (50 runs):
3867.143019 task-clock # 0.577 CPUs utilized ( +- 0.10% )
200,008 context-switches # 0.052 M/sec ( +- 0.00% )
0 CPU-migrations # 0.000 M/sec ( +- 56.54% )
135 page-faults # 0.000 M/sec ( +- 0.17% )
7,594,083,776 cycles # 1.964 GHz ( +- 0.12% )
2,775,221,867 stalled-cycles-frontend # 36.54% frontend cycles idle ( +- 0.19% )
1,251,931,725 stalled-cycles-backend # 16.49% backend cycles idle ( +- 0.36% )
8,574,447,382 instructions # 1.13 insns per cycle
# 0.32 stalled cycles per insn ( +- 0.09% )
1,751,600,855 branches # 452.944 M/sec ( +- 0.09% )
36,098,438 branch-misses # 2.06% of all branches ( +- 0.16% )
6.698065282 seconds time elapsed ( +- 0.05% )
+patch, cgroup disabled, drop_caches:
Performance counter stats for './pipe-test-100k' (50 runs):
3857.654582 task-clock # 0.577 CPUs utilized ( +- 0.10% )
200,009 context-switches # 0.052 M/sec ( +- 0.00% )
0 CPU-migrations # 0.000 M/sec ( +- 78.57% )
135 page-faults # 0.000 M/sec ( +- 0.23% )
7,584,913,316 cycles # 1.966 GHz ( +- 0.11% )
2,771,130,327 stalled-cycles-frontend # 36.53% frontend cycles idle ( +- 0.17% )
1,263,203,011 stalled-cycles-backend # 16.65% backend cycles idle ( +- 0.40% )
8,574,734,269 instructions # 1.13 insns per cycle
# 0.32 stalled cycles per insn ( +- 0.09% )
1,751,597,037 branches # 454.058 M/sec ( +- 0.09% )
36,113,467 branch-misses # 2.06% of all branches ( +- 0.14% )
6.688379749 seconds time elapsed ( +- 0.04% )
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