Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q7

Mark_H_Johnson_at_raytheon.com
Date: 09/02/04

  • Next message: Ingo Molnar: "Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q9" 
    To: Ingo Molnar <mingo@elte.hu>
Date:	Thu, 2 Sep 2004 08:18:02 -0500

    >(you mean 500+ usec, correct?)
    >
    >there's no way the scheduler can have 500 usecs of overhead going from
    >dequeue_task() to __switch_to(): we have all interrupts disabled and
    >take zero locks! This is almost certainly some hardware effect (i
    >described some possibilities and tests a couple of mails earlier).
    >
    >In any case, please enable nmi_watchdog=1 so that we can see (in -Q7)
    >what happens on the other CPUs during such long delays.

    Booted with nmi_watchdog=1, saw the kernel message indicating that
    NMI was checked OK.

    The first trace looks something like this...

    latency 518 us, entries: 79
    ...
    started at schedule+0x51/0x740
    ended at schedule+0x337/0x740

    00000001 0.000ms (+0.000ms): schedule (io_schedule)
    00000001 0.000ms (+0.000ms): sched_clock (schedule)
    00010001 0.478ms (+0.478ms): do_nmi (sched_clock)
    00010001 0.478ms (+0.000ms): do_nmi (<08049b21>)
    00010001 0.482ms (+0.003ms): profile_tick (nmi_watchdog_tick)
    ...
    and a few entries later ends up at do_IRQ (sched_clock).

    The second trace goes from dequeue_task to __switch_to with a
    similar pattern - the line with do_nmi has +0.282ms duration and
    the line notifier_call_chain (profile_hook) as +0.135ms duration.

    I don't see how this provides any additional information but will
    provide several additional traces when the test gets done in a
    few minutes.

    --Mark H Johnson
      <mailto:Mark_H_Johnson@raytheon.com>

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