Re: [PATCH V3]hrtimer: Fix a performance regression by disablereprogramming in remove_hrtimer

From: Mike Galbraith
Date: Tue Aug 06 2013 - 03:47:07 EST

(CCs Intel folks)

On Tue, 2013-08-06 at 09:29 +0200, Mike Galbraith wrote:
> On Tue, 2013-07-30 at 11:35 +0200, Peter Zijlstra wrote:
>
> > It would be good if you could do what Thomas suggested and look at which
> > timer is actually active during your workload.
>
> Rebuilding regression test trees, some pipe-test results...
>
> I'm missing mwait_idle() rather a lot on Q6600, and at 3.8, E5620 took a
> severe NOHZ drubbing from the menu governor.
>
> pipe-test, scheduling cross core
>
> NOTE: nohz is throttled here (patchlet below), as to not eat horrible
> microidle cost, see E5620 v3.7.10-nothrottle below.
>
> Q6600
> v3.8.13 500.6 KHz 1.000
> v3.9.11 422.4 KHz .843
> v3.10.4 420.2 KHz .839
> v3.11-rc3-4-g36f571e 404.7 KHz .808
>
> Q6600 3.9 regression:
> guilty party is 69fb3676 x86 idle: remove mwait_idle() and "idle=mwait" cmdline param
> halt sucks, HTH does one activate mwait_idle_with_hints() [processor_idle()] for core2 boxen?
>
> E5620 +write 0 -> /dev/cpu_dma_latency, hold open
> v3.7.10 578.5 KHz 1.000 675.4 KHz 1.000
> v3.7.10-nothrottle 366.7 KHz .633 395.0 KHz .584
> v3.8.13 468.3 KHz .809 690.0 KHz 1.021
> v3.8.13 idle=mwait 595.1 KHz 1.028 NA
> v3.9.11 462.0 KHz .798 691.1 KHz 1.023
> v3.10.4 419.4 KHz .724 570.8 KHz .845
> v3.11-rc3-4-g36f571e 400.1 KHz .691 538.5 KHz .797
>
> E5620 3.8 regression:
> guilty party: 69a37bea cpuidle: Quickly notice prediction failure for repeat mode
>
>
> Q6600 (2.4 GHz core2 quad)
> v3.11-rc3-4-g36f571e v3.8.13
> 7.97% [k] reschedule_interrupt 8.63% [k] __schedule
> 6.27% [k] __schedule 6.07% [k] native_sched_clock
> 4.74% [k] native_sched_clock 4.96% [k] system_call
> 4.23% [k] _raw_spin_lock_irqsave 4.30% [k] _raw_spin_lock_irqsave
> 3.39% [k] system_call 4.06% [k] resched_task
> 2.89% [k] sched_clock_local 3.44% [k] sched_clock_local
> 2.79% [k] mutex_lock 3.39% [k] pipe_read
> 2.57% [k] pipe_read 3.21% [k] mutex_lock
> 2.55% [k] __switch_to 2.98% [k] read_tsc
> 2.24% [k] read_tsc 2.87% [k] __switch_to
>
>
> E5620 (2.4 GHz Westmere quad)
> v3.7.10 v3.7.10-nothrottle v3.7.10-nothrottle
> 8.01% [k] __schedule 25.80% [k] _raw_spin_unlock_irqrestore 21.80% [k] _raw_spin_unlock_irqrestore
> 4.49% [k] resched_tas 4.64% [k] __hrtimer_start_range_ns - _raw_spin_unlock_irqrestore
> 3.94% [k] mutex_lock 4.62% [k] timerqueue_add + 37.94% __hrtimer_start_range_ns
> 3.44% [k] __switch_to 4.54% [k] __schedule 19.69% hrtimer_cancel
> 3.18% [k] menu_select 2.84% [k] enqueue_hrtimer tick_nohz_restart
> 3.05% [k] copy_user_generic_string 2.64% [k] resched_task tick_nohz_idle_exit
> 3.02% [k] task_waking_fair 2.29% [k] _raw_spin_lock_irqsave cpu_idle
> 2.91% [k] mutex_unlock 2.28% [k] mutex_lock start_secondary
> 2.82% [k] pipe_read 1.96% [k] __switch_to + 16.05% hrtimer_start_range_ns
> 2.32% [k] ktime_get_real 1.73% [k] menu_select 15.46% hrtimer_start
> tick_nohz_stop_sched_tick
> __tick_nohz_idle_enter
> tick_nohz_idle_enter
> cpu_idle
> start_secondary
> 6.37% hrtimer_try_to_cancel
> hrtimer_cancel
> tick_nohz_restart
> tick_nohz_idle_exit
> cpu_idle
> start_secondary
>
> v3.8.13 v3.8.13 idle=mwait v3.8.13 (throttled, but menu gov bites.. HARD)
> 23.16% [k] _raw_spin_unlock_irqrestore 8.35% [k] __schedule - 22.91% [k] _raw_spin_unlock_irqrestore
> 4.93% [k] __schedule 6.49% [k] __switch_to - _raw_spin_unlock_irqrestore
> 3.42% [k] resched_task 5.71% [k] resched_task - 47.26% hrtimer_try_to_cancel
> 3.27% [k] __switch_to 4.64% [k] mutex_lock hrtimer_cancel
> 3.05% [k] mutex_lock 3.48% [k] copy_user_generic_string menu_hrtimer_cancel
> 2.32% [k] copy_user_generic_string 3.15% [k] task_waking_fair tick_nohz_idle_exit
> 2.30% [k] _raw_spin_lock_irqsave 3.13% [k] pipe_read cpu_idle
> 2.15% [k] pipe_read 2.61% [k] mutex_unlock start_secondary
> 2.15% [k] task_waking_fair 2.54% [k] finish_task_switch - 40.01% __hrtimer_start_range_ns
> 2.08% [k] ktime_get 2.29% [k] _raw_spin_lock_irqsave hrtimer_start
> 1.87% [k] mutex_unlock 1.91% [k] idle_cpu menu_select
> 1.76% [k] finish_task_switch 1.84% [k] __wake_up_common cpuidle_idle_call
> cpu_idle
> start_secondary
>
> v3.9.11
> 18.67% [k] _raw_spin_unlock_irqrestore
> 4.36% [k] __schedule
> 3.66% [k] __switch_to
> 3.13% [k] mutex_lock
> 2.97% [k] __hrtimer_start_range_ns
> 2.69% [k] _raw_spin_lock_irqsave
> 2.38% [k] copy_user_generic_string
> 2.34% [k] hrtimer_reprogram.isra.32
> 2.34% [k] task_waking_fair
> 2.25% [k] ktime_get
> 2.14% [k] pipe_read
> 1.98% [k] menu_select
>
> v3.10.4
> 20.42% [k] _raw_spin_unlock_irqrestore
> 4.75% [k] __schedule
> 4.42% [k] reschedule_interrupt <== appears in 3.10, guilty party as yet unknown
> 3.52% [k] __switch_to
> 3.27% [k] resched_task
> 2.64% [k] cpuidle_enter_state
> 2.63% [k] _raw_spin_lock_irqsave
> 2.04% [k] copy_user_generic_string
> 2.00% [k] cpu_idle_loop
> 1.97% [k] mutex_lock
> 1.90% [k] ktime_get
> 1.75% [k] task_waking_fair
>
> v3.11-rc3-4-g36f571e
> 18.96% [k] _raw_spin_unlock_irqrestore
> 4.84% [k] __schedule
> 4.69% [k] reschedule_interrupt
> 3.75% [k] __switch_to
> 2.62% [k] _raw_spin_lock_irqsave
> 2.43% [k] cpuidle_enter_state
> 2.28% [k] resched_task
> 2.20% [k] cpu_idle_loop
> 1.97% [k] copy_user_generic_string
> 1.88% [k] ktime_get
> 1.81% [k] task_waking_fair
> 1.75% [k] mutex_lock
>
> sched: ratelimit nohz
>
> Entering nohz code on every micro-idle is too expensive to bear.
>
> Signed-off-by: Mike Galbraith <efault@xxxxxx>
>
> ---
> include/linux/sched.h | 5 +++++
> kernel/sched/core.c | 5 +++++
> kernel/time/tick-sched.c | 2 +-
> 3 files changed, 11 insertions(+), 1 deletion(-)
>
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -235,9 +235,14 @@ extern int runqueue_is_locked(int cpu);
> extern void nohz_balance_enter_idle(int cpu);
> extern void set_cpu_sd_state_idle(void);
> extern int get_nohz_timer_target(void);
> +extern int sched_needs_cpu(int cpu);
> #else
> static inline void nohz_balance_enter_idle(int cpu) { }
> static inline void set_cpu_sd_state_idle(void) { }
> +static inline int sched_needs_cpu(int cpu)
> +{
> + return 0;
> +}
> #endif
>
> /*
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -650,6 +650,11 @@ static inline bool got_nohz_idle_kick(vo
> return false;
> }
>
> +int sched_needs_cpu(int cpu)
> +{
> + return cpu_rq(cpu)->avg_idle < sysctl_sched_migration_cost;
> +}
> +
> #else /* CONFIG_NO_HZ_COMMON */
>
> static inline bool got_nohz_idle_kick(void)
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -548,7 +548,7 @@ static ktime_t tick_nohz_stop_sched_tick
> time_delta = timekeeping_max_deferment();
> } while (read_seqretry(&jiffies_lock, seq));
>
> - if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
> + if (sched_needs_cpu(cpu) || rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
> arch_needs_cpu(cpu) || irq_work_needs_cpu()) {
> next_jiffies = last_jiffies + 1;
> delta_jiffies = 1;
>
>


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