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Subject: [RT] possible bug in trace_start_sched_wakeup
From: Steven Rostedt <rostedt@goodmis.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: LKML <linux-kernel@vger.kernel.org>
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Date: Thu, 26 Jan 2006 20:57:02 -0500
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Ingo,

I've been agonizing over the latency code, and have a question about
__trace_start_sched_wakup.

Here we have:

void __trace_start_sched_wakeup(struct task_struct *p)
{
	struct cpu_trace *tr;
	int cpu;

	if (trace_user_triggered || !wakeup_timing)
		return;

	spin_lock(&sch.trace_lock);
	if (sch.task && (sch.task->prio >= p->prio))
		goto out_unlock;


I don't get the sch.task->prio >= p->prio.  Here the lower the number
the greater the priority.  So this if statement is saying:

If sch.task is either NULL or if p is greater in priority than or equal
to the priority of sch.task then quit.

Then again later in  trace_stop_sched_switched:

		if (sch.task && (sch.task->prio >= p->prio))
			sch.task = NULL;

Again, if p is a higher priority than sch.task we set sch.task to NULL??


What am I missing here?

Thanks,

-- Steve