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SubjectRe: [PATCH] tracing: Add task activate/deactivate tracepoints
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Expect slow responses from me today. It's a US Holiday.


On Mon, 2010-05-31 at 18:18 +0200, Peter Zijlstra wrote:
> 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

I guess this could work. I can't think of anything that would cause this
to fail. But this is not exactly what the CREATE_TRACE_POINTS macro was
for.

Maybe we could make a CREATE_UTIL_FUNCTIONS macro that the
define_trace.h can unset like it does with CREATE_TRACE_POINTS before
recursively including the trace headers.

Maybe I'm a bit paranoid, but I'm a little nervous to extend the
CREATE_TRACE_POINTS macro to be used within the header to create utility
functions, although, currently I don't think there's anything
technically wrong in doing so.

-- Steve

> +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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