Re: 2.6.13-rt12: irqs hard off for 657 usecs

From: Lee Revell
Date: Tue Oct 11 2005 - 11:29:28 EST

On Tue, 2005-10-11 at 13:20 +0200, Ingo Molnar wrote:
> * Lee Revell <rlrevell@xxxxxxxxxxx> wrote:
> > Something appears to have disabled IRQs for 657 usecs.
> how hard is it to reproduce this latency?

Very easy. Here's the current max latency.

The max latency is close to the period of the timer IRQ. So either it's
an instrumentation bug or something really disables IRQs for up to 1/HZ

preemption latency trace v1.1.5 on 2.6.13-rt12
latency: 928 us, #1359/1359, CPU#0 | (M:rt VP:0, KP:1, SP:1 HP:1)
| task: softirq-tasklet-7 (uid:0 nice:0 policy:1 rt_prio:1)

_------=> CPU#
/ _-----=> irqs-off
| / _----=> need-resched
|| / _---=> hardirq/softirq
||| / _--=> preempt-depth
|||| /
||||| delay
cmd pid ||||| time | caller
\ / ||||| \ | /
kswapd0-100 0Dnh2 0us : __trace_start_sched_wakeup (try_to_wake_up)
kswapd0-100 0Dnh2 1us : __trace_start_sched_wakeup <softirq--7> (62 0)
kswapd0-100 0Dnh1 1us : preempt_schedule (__trace_start_sched_wakeup)
kswapd0-100 0Dnh1 2us : try_to_wake_up <softirq--7> (62 73)
kswapd0-100 0Dnh. 2us : check_raw_flags (try_to_wake_up)
kswapd0-100 0Dnh. 3us : preempt_schedule (try_to_wake_up)
kswapd0-100 0Dnh. 4us : wake_up_process_mutex (__up_mutex_waiter_savestate)
kswapd0-100 0Dnh. 4us+: check_raw_flags (up_mutex)
kswapd0-100 0Dn.. 8us : memmove (cache_flusharray)
kswapd0-100 0Dn.. 8us : memcpy (memmove)
kswapd0-100 0Dn.. 9us : _spin_unlock (kmem_cache_free)
kswapd0-100 0Dn.. 9us : up_mutex (_spin_unlock)
kswapd0-100 0Dnh. 10us : check_raw_flags (up_mutex)
kswapd0-100 0Dn.. 10us : clear_inode (dispose_list)
kswapd0-100 0Dn.. 11us : __might_sleep (clear_inode)
kswapd0-100 0Dn.. 12us : invalidate_inode_buffers (clear_inode)
kswapd0-100 0Dn.. 12us : inode_has_buffers (invalidate_inode_buffers)
kswapd0-100 0Dn.. 13us : __might_sleep (clear_inode)
kswapd0-100 0Dn.. 13us : ext3_clear_inode (clear_inode)
kswapd0-100 0Dn.. 14us : ext3_discard_reservation (ext3_clear_inode)
kswapd0-100 0Dn.. 15us : kfree (ext3_clear_inode)
kswapd0-100 0Dn.. 15us : _spin_lock (dispose_list)
kswapd0-100 0Dn.. 16us : _spin_unlock (dispose_list)
kswapd0-100 0Dn.. 17us : up_mutex (_spin_unlock)
kswapd0-100 0Dnh. 17us : check_raw_flags (up_mutex)
kswapd0-100 0Dn.. 18us : wake_up_inode (dispose_list)
kswapd0-100 0Dn.. 18us : wake_up_bit (wake_up_inode)
kswapd0-100 0Dn.. 19us : bit_waitqueue (wake_up_bit)
kswapd0-100 0Dn.. 20us : __wake_up_bit (wake_up_bit)

This part repeats:

kswapd0-100 0Dn.. 20us : destroy_inode (dispose_list)
kswapd0-100 0Dn.. 21us : inode_has_buffers (destroy_inode)
kswapd0-100 0Dn.. 22us : dummy_inode_free_security (destroy_inode)
kswapd0-100 0Dn.. 22us : ext3_destroy_inode (destroy_inode)
kswapd0-100 0Dn.. 23us : kmem_cache_free (ext3_destroy_inode)
kswapd0-100 0Dn.. 23us : __local_save_flags (kmem_cache_free)
kswapd0-100 0Dn.. 24us : _spin_lock (kmem_cache_free)
kswapd0-100 0Dn.. 24us : _spin_unlock (kmem_cache_free)
kswapd0-100 0Dn.. 25us : up_mutex (_spin_unlock)
kswapd0-100 0Dnh. 25us : check_raw_flags (up_mutex)
kswapd0-100 0Dn.. 26us : clear_inode (dispose_list)
kswapd0-100 0Dn.. 27us : __might_sleep (clear_inode)
kswapd0-100 0Dn.. 27us : invalidate_inode_buffers (clear_inode)
kswapd0-100 0Dn.. 28us : inode_has_buffers (invalidate_inode_buffers)
kswapd0-100 0Dn.. 29us : __might_sleep (clear_inode)
kswapd0-100 0Dn.. 29us : ext3_clear_inode (clear_inode)
kswapd0-100 0Dn.. 30us : ext3_discard_reservation (ext3_clear_inode)
kswapd0-100 0Dn.. 31us : kfree (ext3_clear_inode)
kswapd0-100 0Dn.. 31us : _spin_lock (dispose_list)
kswapd0-100 0Dn.. 33us : _spin_unlock (dispose_list)
kswapd0-100 0Dn.. 33us : up_mutex (_spin_unlock)
kswapd0-100 0Dnh. 34us : check_raw_flags (up_mutex)
kswapd0-100 0Dn.. 34us : wake_up_inode (dispose_list)
kswapd0-100 0Dn.. 35us : wake_up_bit (wake_up_inode)
kswapd0-100 0Dn.. 36us : bit_waitqueue (wake_up_bit)
kswapd0-100 0Dn.. 36us : __wake_up_bit (wake_up_bit)

kswapd0-100 0Dn.. 37us : destroy_inode (dispose_list)
kswapd0-100 0Dn.. 38us : inode_has_buffers (destroy_inode)


Finally the timer interrupt saves the day:

kswapd0-100 0Dnh. 859us : do_IRQ (c0150297 0 0)
kswapd0-100 0Dnh1 861us+: mask_and_ack_8259A (__do_IRQ)
kswapd0-100 0Dnh1 865us : check_raw_flags (mask_and_ack_8259A)
kswapd0-100 0Dnh1 866us : preempt_schedule (mask_and_ack_8259A)
kswapd0-100 0Dnh1 866us : redirect_hardirq (__do_IRQ)
kswapd0-100 0Dnh. 867us : preempt_schedule (__do_IRQ)
kswapd0-100 0Dnh. 868us : handle_IRQ_event (__do_IRQ)
kswapd0-100 0Dnh. 869us : timer_interrupt (handle_IRQ_event)
kswapd0-100 0Dnh1 869us+: mark_offset_pmtmr (timer_interrupt)
kswapd0-100 0Dnh1 872us : preempt_schedule (mark_offset_pmtmr)
kswapd0-100 0Dnh1 873us : do_timer (timer_interrupt)
kswapd0-100 0Dnh1 874us : update_process_times (timer_interrupt)
kswapd0-100 0Dnh1 874us : account_system_time (update_process_times)
kswapd0-100 0Dnh1 876us : acct_update_integrals (account_system_time)
kswapd0-100 0Dnh1 876us : update_mem_hiwater (account_system_time)
kswapd0-100 0Dnh1 877us : run_local_timers (update_process_times)
kswapd0-100 0Dnh1 878us : raise_softirq (run_local_timers)
kswapd0-100 0Dnh1 878us : check_raw_flags (raise_softirq)
kswapd0-100 0Dnh1 879us : rcu_pending (update_process_times)
kswapd0-100 0Dnh1 880us : rcu_check_callbacks (update_process_times)
kswapd0-100 0Dnh1 880us : rcu_try_flip (rcu_check_callbacks)
kswapd0-100 0Dnh1 881us : check_raw_flags (rcu_try_flip)
kswapd0-100 0Dnh1 882us : preempt_schedule (rcu_try_flip)
kswapd0-100 0Dnh2 882us : __rcu_advance_callbacks (rcu_check_callbacks)
kswapd0-100 0Dnh1 883us : check_raw_flags (rcu_check_callbacks)
kswapd0-100 0Dnh1 884us : preempt_schedule (rcu_check_callbacks)
kswapd0-100 0Dnh1 885us : __tasklet_schedule (rcu_check_callbacks)
kswapd0-100 0Dnh1 885us : check_raw_flags (__tasklet_schedule)
kswapd0-100 0Dnh1 886us : scheduler_tick (update_process_times)
kswapd0-100 0Dnh1 887us : sched_clock (scheduler_tick)
kswapd0-100 0Dnh2 888us : task_timeslice (scheduler_tick)
kswapd0-100 0Dnh1 889us : preempt_schedule (scheduler_tick)
kswapd0-100 0Dnh1 890us : smp_local_timer_interrupt (timer_interrupt)
kswapd0-100 0Dnh. 891us : preempt_schedule (timer_interrupt)
kswapd0-100 0Dnh1 892us : note_interrupt (__do_IRQ)
kswapd0-100 0Dnh1 892us : enable_8259A_irq (__do_IRQ)
kswapd0-100 0Dnh1 894us : check_raw_flags (enable_8259A_irq)
kswapd0-100 0Dnh1 895us : preempt_schedule (enable_8259A_irq)
kswapd0-100 0Dnh. 896us : preempt_schedule (__do_IRQ)
kswapd0-100 0Dnh. 896us : irq_exit (do_IRQ)
kswapd0-100 0Dnh1 897us : do_softirq (irq_exit)
kswapd0-100 0Dnh1 898us : __do_softirq (do_softirq)
kswapd0-100 0Dnh1 899us : trigger_softirqs (__do_softirq)
kswapd0-100 0Dnh1 899us : wakeup_softirqd (trigger_softirqs)
kswapd0-100 0Dnh1 900us : wake_up_process (wakeup_softirqd)
kswapd0-100 0Dnh1 901us : check_preempt_wakeup (wake_up_process)
kswapd0-100 0Dnh1 901us : try_to_wake_up (wake_up_process)
kswapd0-100 0Dnh2 902us : activate_task (try_to_wake_up)
kswapd0-100 0Dnh2 903us : sched_clock (activate_task)
kswapd0-100 0Dnh2 904us : recalc_task_prio (activate_task)
kswapd0-100 0Dnh2 905us : __recalc_task_prio (recalc_task_prio)
kswapd0-100 0Dnh2 905us : __recalc_task_prio <<...>-3> (62 62)
kswapd0-100 0Dnh2 906us : activate_task <<...>-3> (62 3)
kswapd0-100 0Dnh2 907us : enqueue_task (activate_task)
kswapd0-100 0Dnh2 908us : __trace_start_sched_wakeup (try_to_wake_up)
kswapd0-100 0Dnh2 909us : preempt_schedule (__trace_start_sched_wakeup)
kswapd0-100 0Dnh2 909us : try_to_wake_up <<...>-3> (62 73)
kswapd0-100 0Dnh1 910us : check_raw_flags (try_to_wake_up)
kswapd0-100 0Dnh1 910us : preempt_schedule (try_to_wake_up)
kswapd0-100 0Dnh1 911us : wake_up_process (wakeup_softirqd)
kswapd0-100 0Dnh1 912us : wakeup_softirqd (trigger_softirqs)
kswapd0-100 0Dnh1 912us : wake_up_process (wakeup_softirqd)
kswapd0-100 0Dnh1 913us : check_preempt_wakeup (wake_up_process)
kswapd0-100 0Dnh1 913us : try_to_wake_up (wake_up_process)
kswapd0-100 0Dnh1 915us : check_raw_flags (try_to_wake_up)
kswapd0-100 0Dnh1 915us : preempt_schedule (try_to_wake_up)
kswapd0-100 0Dnh1 916us : wake_up_process (wakeup_softirqd)
kswapd0-100 0Dnh1 917us : check_raw_flags (do_softirq)
kswapd0-100 0Dnh. 917us : preempt_schedule_irq (need_resched)
kswapd0-100 0Dnh. 918us : __schedule (preempt_schedule_irq)
kswapd0-100 0Dnh. 919us : profile_hit (__schedule)
kswapd0-100 0Dnh1 920us : sched_clock (__schedule)
softirq--7 0Dnh2 923us : __switch_to (__schedule)
softirq--7 0Dnh2 924us : __schedule <kswapd0-100> (73 62)
softirq--7 0...1 925us : trace_stop_sched_switched (__schedule)
softirq--7 0Dnh2 926us : trace_stop_sched_switched <softirq--7> (62 0)
softirq--7 0Dnh2 927us : trace_stop_sched_switched (__schedule)

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