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    SubjectRe: [PATCH] tracing: Add task activate/deactivate tracepoints
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    On Mon, 2010-05-31 at 16:48 +0200, Frederic Weisbecker wrote:
    > > Should we maybe cure this and rely on sched_switch() to detect sleeps?
    > > It seems natural since only the current task can go to sleep, its just
    > > that the whole preempt state gets a bit iffy.

    How about something like the below?

    Steve, is that proper usage of CREATE_TRACE_POINT?

    ---
    Subject: sched, trace: Fix sched_switch() prev_state argument
    From: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Date: Mon May 31 18:13:25 CEST 2010

    For CONFIG_PREEMPT=y kernels the sched_switch(.prev_state) argument
    isn't useful because we can get preempted with current->state !=
    TASK_RUNNING without actually getting removed from the runqueue.

    Cure this by treating all preempted tasks as runnable from the
    tracer's point of view.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    include/trace/events/sched.h | 19 ++++++++++++++++++-
    1 file changed, 18 insertions(+), 1 deletion(-)

    Index: linux-2.6/include/trace/events/sched.h
    ===================================================================
    --- linux-2.6.orig/include/trace/events/sched.h
    +++ linux-2.6/include/trace/events/sched.h
    @@ -115,6 +115,23 @@ DEFINE_EVENT(sched_wakeup_template, sche
    TP_PROTO(struct task_struct *p, int success),
    TP_ARGS(p, success));

    +#ifdef CREATE_TRACE_POINTS
    +static inline long __trace_sched_switch_state(struct task_struct *p)
    +{
    + long state = p->state;
    +
    +#ifdef CONFIG_PREEMPT
    + /*
    + * For all intents and purposes a preempted task is a running task.
    + */
    + if (task_thread_info(p)->preempt_count & PREEMPT_ACTIVE)
    + state = TASK_RUNNING;
    +#endif
    +
    + return state;
    +}
    +#endif
    +
    /*
    * Tracepoint for task switches, performed by the scheduler:
    */
    @@ -139,7 +156,7 @@ TRACE_EVENT(sched_switch,
    memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
    __entry->prev_pid = prev->pid;
    __entry->prev_prio = prev->prio;
    - __entry->prev_state = prev->state;
    + __entry->prev_state = __trace_sched_switch_state(prev);
    memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
    __entry->next_pid = next->pid;
    __entry->next_prio = next->prio;


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