2.6.14-rt22 (and mainline) excessive latency

Lee Revell
2005-12-20T00:38:04Z

I captured this 3+ ms latency trace when killing a process with a few
thousand threads. Can a cond_resched be added to this code path?

preemption latency trace v1.1.5 on 2.6.14-rt22
--------------------------------------------------------------------
latency: 3321 us, #2830/2830, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0)
-----------------
| task: softirq-timer/0-3 (uid:0 nice:0 policy:1 rt_prio:1)
-----------------

_------=> CPU#
/ _-----=> irqs-off
| / _----=> need-resched
|| / _---=> hardirq/softirq
||| / _--=> preempt-depth
|||| /
||||| delay
cmd pid ||||| time | caller
\ / ||||| \ | /
bash-17992 0D.h2 1us : __trace_start_sched_wakeup (try_to_wake_up)
bash-17992 0D.h2 1us : __trace_start_sched_wakeup <<...>-3> (62 0)
bash-17992 0D.h. 2us : wake_up_process (wakeup_softirqd)
bash-17992 0D.h. 3us : rcu_check_callbacks (update_process_times)
bash-17992 0D.h. 3us : idle_cpu (rcu_check_callbacks)
bash-17992 0D.h. 4us : __tasklet_schedule (rcu_check_callbacks)
bash-17992 0D.h. 5us : wakeup_softirqd (__tasklet_schedule)
bash-17992 0D.h. 6us : wake_up_process (wakeup_softirqd)
bash-17992 0D.h. 6us : try_to_wake_up (wake_up_process)
bash-17992 0D.h1 7us : activate_task (try_to_wake_up)
bash-17992 0D.h1 8us : sched_clock (activate_task)
bash-17992 0D.h1 9us : recalc_task_prio (activate_task)
bash-17992 0D.h1 10us : __recalc_task_prio (recalc_task_prio)
bash-17992 0D.h1 10us : __recalc_task_prio <<...>-7> (62 62)
bash-17992 0D.h1 11us : activate_task <<...>-7> (62 d)
bash-17992 0D.h1 12us : enqueue_task (activate_task)
bash-17992 0D.h1 12us : __trace_start_sched_wakeup (try_to_wake_up)
bash-17992 0D.h. 14us : wake_up_process (wakeup_softirqd)
bash-17992 0D.h. 14us : scheduler_tick (update_process_times)
bash-17992 0D.h. 15us : sched_clock (scheduler_tick)
bash-17992 0D.h1 16us : task_timeslice (scheduler_tick)
bash-17992 0D.h. 17us : run_posix_cpu_timers (update_process_times)
bash-17992 0D.h1 19us : note_interrupt (__do_IRQ)
bash-17992 0D.h1 19us : end_8259A_irq (__do_IRQ)
bash-17992 0D.h1 20us+: enable_8259A_irq (end_8259A_irq)
bash-17992 0Dnh1 22us : irq_exit (do_IRQ)
bash-17992 0Dn.1 23us < (608)
bash-17992 0.n.1 24us : eligible_child (do_wait)
bash-17992 0.n.1 25us : eligible_child (do_wait)
bash-17992 0.n.1 26us : eligible_child (do_wait)
bash-17992 0.n.1 28us : eligible_child (do_wait)
bash-17992 0.n.1 29us : eligible_child (do_wait)

[ 3000+ of these deleted ]

bash-17992 0.n.1 3296us : eligible_child (do_wait)
bash-17992 0.n.1 3297us : eligible_child (do_wait)
bash-17992 0.n.1 3298us : eligible_child (do_wait)
bash-17992 0.n.1 3299us : eligible_child (do_wait)
bash-17992 0.n.1 3300us : eligible_child (do_wait)
bash-17992 0.n.1 3301us : eligible_child (do_wait)
bash-17992 0.n.1 3303us : eligible_child (do_wait)
bash-17992 0.n.1 3304us : next_thread (do_wait)
bash-17992 0.n.. 3305us : preempt_schedule (do_wait)
bash-17992 0Dn.. 3306us : __schedule (preempt_schedule)
bash-17992 0Dn.. 3307us : profile_hit (__schedule)
bash-17992 0Dn.1 3308us+: sched_clock (__schedule)
<...>-3 0D..2 3314us+: __switch_to (__schedule)
<...>-3 0D..2 3316us : __schedule <bash-17992> (73 62)
<...>-3 0...1 3317us : trace_stop_sched_switched (__schedule)
<...>-3 0D..2 3318us : trace_stop_sched_switched <<...>-3> (62 0)
<...>-3 0D..2 3320us : trace_stop_sched_switched (__schedule)