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 <efa...@gmx.de> --- 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/