Messages in this thread | | | Subject | Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q5 | From | Thomas Charbonnel <> | Date | Tue, 31 Aug 2004 21:23:48 +0200 |
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Ingo Molnar wrote :
(...) > > and a weird one with do_timer (called from do_IRQ) taking more than 1ms > > to complete : > > http://www.undata.org/~thomas/do_irq.trace > > hm, indeed this is a weird one. 1 msec is too close to the timer > frequency to be accidental. According to the trace: > > 00010000 0.002ms (+0.000ms): timer_interrupt (generic_handle_IRQ_event) > 00010001 0.002ms (+0.000ms): mark_offset_tsc (timer_interrupt) > 00010001 1.028ms (+1.025ms): do_timer (timer_interrupt) > 00010001 1.028ms (+0.000ms): update_process_times (do_timer) > > the latency happened between the beginning of mark_offset_tsc() and the > calling of do_timer() - i.e. the delay happened somewhere within > mark_offset_tsc() itself. Is this an SMP system? > > Ingo
It isn't an SMP system, but here are some other traces that can prove useful : preemption latency trace v1.0.2 ------------------------------- latency: 567 us, entries: 35 (35) ----------------- | task: swapper/0, uid:0 nice:0 policy:0 rt_prio:0 ----------------- => started at: do_IRQ+0x19/0x190 => ended at: do_IRQ+0x13d/0x190 =======> 00010000 0.000ms (+0.000ms): do_IRQ (common_interrupt) 00010000 0.000ms (+0.000ms): do_IRQ (default_idle) 00010001 0.000ms (+0.000ms): mask_and_ack_8259A (do_IRQ) 00010001 0.002ms (+0.002ms): generic_redirect_hardirq (do_IRQ) 00010000 0.002ms (+0.000ms): generic_handle_IRQ_event (do_IRQ) 00010000 0.002ms (+0.000ms): timer_interrupt (generic_handle_IRQ_event) 00010001 0.003ms (+0.000ms): mark_offset_tsc (timer_interrupt) 00010001 0.562ms (+0.559ms): do_timer (timer_interrupt) 00010001 0.562ms (+0.000ms): update_process_times (do_timer) 00010001 0.562ms (+0.000ms): update_one_process (update_process_times) 00010001 0.562ms (+0.000ms): run_local_timers (update_process_times) 00010001 0.562ms (+0.000ms): raise_softirq (update_process_times) 00010001 0.562ms (+0.000ms): scheduler_tick (update_process_times) 00010001 0.562ms (+0.000ms): sched_clock (scheduler_tick) 00010001 0.563ms (+0.000ms): update_wall_time (do_timer) 00010001 0.563ms (+0.000ms): update_wall_time_one_tick (update_wall_time) 00010001 0.563ms (+0.000ms): profile_tick (timer_interrupt) 00010001 0.563ms (+0.000ms): profile_hook (profile_tick) 00010002 0.563ms (+0.000ms): notifier_call_chain (profile_hook) 00010001 0.564ms (+0.000ms): profile_hit (timer_interrupt) 00010001 0.564ms (+0.000ms): generic_note_interrupt (do_IRQ) 00010001 0.564ms (+0.000ms): end_8259A_irq (do_IRQ) 00010001 0.564ms (+0.000ms): enable_8259A_irq (do_IRQ) 00000001 0.565ms (+0.000ms): do_softirq (do_IRQ) 00000001 0.565ms (+0.000ms): __do_softirq (do_softirq) 00000001 0.565ms (+0.000ms): wake_up_process (do_softirq) 00000001 0.565ms (+0.000ms): try_to_wake_up (wake_up_process) 00000001 0.566ms (+0.000ms): task_rq_lock (try_to_wake_up) 00000002 0.566ms (+0.000ms): activate_task (try_to_wake_up) 00000002 0.566ms (+0.000ms): sched_clock (activate_task) 00000002 0.566ms (+0.000ms): recalc_task_prio (activate_task) 00000002 0.566ms (+0.000ms): effective_prio (recalc_task_prio) 00000002 0.567ms (+0.000ms): enqueue_task (activate_task) 00000001 0.567ms (+0.000ms): preempt_schedule (try_to_wake_up) 00000001 0.567ms (+0.000ms): sub_preempt_count (do_IRQ)
preemption latency trace v1.0.2 ------------------------------- latency: 624 us, entries: 35 (35) ----------------- | task: swapper/0, uid:0 nice:0 policy:0 rt_prio:0 ----------------- => started at: do_IRQ+0x19/0x190 => ended at: do_IRQ+0x13d/0x190 =======> 00010000 0.000ms (+0.000ms): do_IRQ (common_interrupt) 00010000 0.000ms (+0.000ms): do_IRQ (default_idle) 00010001 0.000ms (+0.000ms): mask_and_ack_8259A (do_IRQ) 00010001 0.613ms (+0.612ms): generic_redirect_hardirq (do_IRQ) 00010000 0.613ms (+0.000ms): generic_handle_IRQ_event (do_IRQ) 00010000 0.613ms (+0.000ms): timer_interrupt (generic_handle_IRQ_event) 00010001 0.613ms (+0.000ms): mark_offset_tsc (timer_interrupt) 00010001 0.619ms (+0.005ms): do_timer (timer_interrupt) 00010001 0.619ms (+0.000ms): update_process_times (do_timer) 00010001 0.619ms (+0.000ms): update_one_process (update_process_times) 00010001 0.619ms (+0.000ms): run_local_timers (update_process_times) 00010001 0.619ms (+0.000ms): raise_softirq (update_process_times) 00010001 0.619ms (+0.000ms): scheduler_tick (update_process_times) 00010001 0.619ms (+0.000ms): sched_clock (scheduler_tick) 00010001 0.620ms (+0.000ms): update_wall_time (do_timer) 00010001 0.620ms (+0.000ms): update_wall_time_one_tick (update_wall_time) 00010001 0.620ms (+0.000ms): profile_tick (timer_interrupt) 00010001 0.620ms (+0.000ms): profile_hook (profile_tick) 00010002 0.620ms (+0.000ms): notifier_call_chain (profile_hook) 00010001 0.621ms (+0.000ms): profile_hit (timer_interrupt) 00010001 0.621ms (+0.000ms): generic_note_interrupt (do_IRQ) 00010001 0.621ms (+0.000ms): end_8259A_irq (do_IRQ) 00010001 0.621ms (+0.000ms): enable_8259A_irq (do_IRQ) 00000001 0.622ms (+0.000ms): do_softirq (do_IRQ) 00000001 0.622ms (+0.000ms): __do_softirq (do_softirq) 00000001 0.622ms (+0.000ms): wake_up_process (do_softirq) 00000001 0.622ms (+0.000ms): try_to_wake_up (wake_up_process) 00000001 0.623ms (+0.000ms): task_rq_lock (try_to_wake_up) 00000002 0.623ms (+0.000ms): activate_task (try_to_wake_up) 00000002 0.623ms (+0.000ms): sched_clock (activate_task) 00000002 0.623ms (+0.000ms): recalc_task_prio (activate_task) 00000002 0.623ms (+0.000ms): effective_prio (recalc_task_prio) 00000002 0.623ms (+0.000ms): enqueue_task (activate_task) 00000001 0.624ms (+0.000ms): preempt_schedule (try_to_wake_up) 00000001 0.624ms (+0.000ms): sub_preempt_count (do_IRQ)
As you can see ~1ms was probably an accident, and the latency does not always come from do_timer. The constant is do_IRQ interrupting the idle thread.
Thomas
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