On Mon, 2012-11-12 at 15:53 -0800, John Stultz wrote:
> Cc'ing Steven to see if he can't help understand whats going on here.
I don't trust the trace...
The wake up happened on CPU 2
pulseaud-2106 2d... 1us : 2106:109:R + [003] 2115: 94:S <...>
pulseaud-2106 2d... 2us+: try_to_wake_up <-default_wake_function
Xorg-1278 3d... 1038us : __switch_to_xtra <-__switch_to
Xorg-1278 3d... 1039us : memset <-__switch_to_xtra
kworker/-37 3d... 1040us : finish_task_switch <-__schedule
kworker/-37 3.... 1040us : _raw_spin_lock_irq <-worker_thread
kworker/-37 3d... 1041us : need_more_worker <-worker_thread
kworker/-37 3d... 1041us : process_one_work <-worker_thread
kworker/-37 3.... 1042us : __wake_up <-wakeup_work_handler
A millisecond goes by, Xorg is schedules out for kworker (which I'm sure
is also less in priority). And we don't see any sign of need resched
being set (N).
kworker/-37 3d... 1082us : pick_next_task_idle <-__schedule
<idle>-0 3d... 1083us : finish_task_switch <-__schedule
<idle>-0 3.... 1083us : tick_nohz_idle_enter <-cpu_idle
<idle>-0 3.... 1084us : set_cpu_sd_state_idle <-tick_nohz_idle_enter
<idle>-0 3d... 1084us : __tick_nohz_idle_enter <-tick_nohz_idle_enter
Idle is even scheduled in here!
<idle>-0 3d.h. 9047us : ttwu_do_wakeup <-ttwu_do_activate.constprop.86
<idle>-0 3d.h. 9048us : check_preempt_curr <-ttwu_do_wakeup
<idle>-0 3d.h. 9049us : resched_task <-check_preempt_curr
<idle>-0 3dNh. 9049us : task_woken_rt <-ttwu_do_wakeup
<idle>-0 3dNh. 9050us : ttwu_stat <-try_to_wake_up
<idle>-0 3dNh. 9050us : _raw_spin_unlock_irqrestore <-try_to_wake_up
<idle>-0 3dNh. 9051us : _raw_spin_lock <-__run_hrtimer
During an interrupt (h), we see another wakeup (not sure what this was
for), and the need resched is set (N).
<idle>-0 3dNh. 9053us : lapic_next_event <-clockevents_program_event
<idle>-0 3dNh. 9054us : irq_exit <-smp_apic_timer_interrupt
<idle>-0 3dN.. 9055us : idle_cpu <-irq_exit
<idle>-0 3dN.. 9055us : rcu_irq_exit <-irq_exit
<idle>-0 3dN.. 9056us : rcu_eqs_enter_common.isra.40 <-rcu_irq_exit
<idle>-0 3dN.. 9056us : rcu_prepare_for_idle
<-rcu_eqs_enter_common.isra.40
<idle>-0 3.N.. 9057us : menu_reflect <-cpuidle_idle_call
<idle>-0 3.N.. 9058us : rcu_idle_exit <-cpu_idle
<idle>-0 3dN.. 9058us : rcu_eqs_exit_common.isra.38 <-rcu_idle_exit
<idle>-0 3dN.. 9059us : rcu_cleanup_after_idle
<-rcu_eqs_exit_common.isra.38
<idle>-0 3dN.. 9059us : del_timer <-rcu_cleanup_after_idle
<idle>-0 3.N.. 9060us : tick_nohz_idle_exit <-cpu_idle
<idle>-0 3dN.. 9060us : ktime_get <-tick_nohz_idle_exit
<idle>-0 3dN.. 9061us : tick_do_update_jiffies64 <-tick_nohz_idle_exit
<idle>-0 3dN.. 9061us : update_cpu_load_nohz <-tick_nohz_idle_exit
<idle>-0 3dN.. 9061us : calc_load_exit_idle <-tick_nohz_idle_exit
<idle>-0 3dN.. 9062us : touch_softlockup_watchdog <-tick_nohz_idle_exit
<idle>-0 3dN.. 9062us : tick_nohz_restart <-tick_nohz_idle_exit
<idle>-0 3dN.. 9063us : hrtimer_cancel <-tick_nohz_restart
<idle>-0 3dN.. 9063us : hrtimer_try_to_cancel <-hrtimer_cancel
We exit the interrupt and then do a lot of stuff with interrupts
disabled? Oh, this looks like the exit from idle (rcu_idle_exit is
there). It's doing clean up stuff here.
<idle>-0 3dN.. 9077us : _pick_next_task_rt <-pick_next_task_rt
<idle>-0 3dN.. 9078us : dequeue_pushable_task <-pick_next_task_rt
<idle>-0 3d... 9079us : probe_wakeup_sched_switch <-__schedule
<idle>-0 3d... 9079us : 0:120:R ==> [003] 2115: 94:R <...>
Finally our task is scheduled. But this looks all screwed up to me. I
bet the clocks are not in sync. Do a:
echo global > /sys/kernel/debug/tracing/trace_clock
and this will use a slower clock, but one that is in sync between CPUs.
Also, enable the sched_switch and sched_wakeup trace points too.
cd /sys/kernel/debug/tracing/events/sched
echo 1 > sched_wakeup/enable
echo 1 > sched_switch/enable
-- Steve
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