Commit e8165dbb authored Sep 03, 2009 by Steven Rostedt Committed by Steven Rostedt Sep 04, 2009

tracing: report error in trace if we fail to swap latency buffer



The irqsoff tracer will fail to swap the cpu buffer with the max
buffer if it preempts a commit. Instead of ignoring this, this patch
makes the tracer report it if the last max latency failed due to preempting
a current commit.

The output of the latency tracer will look like this:

 # tracer: irqsoff
 #
 # irqsoff latency trace v1.1.5 on 2.6.31-rc5
 # --------------------------------------------------------------------
 # latency: 112 us, #1/1, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
 #    -----------------
 #    | task: -4281 (uid:0 nice:0 policy:0 rt_prio:0)
 #    -----------------
 #  => started at: save_args
 #  => ended at:   __do_softirq
 #
 #
 #                  _------=> CPU#
 #                 / _-----=> irqs-off
 #                | / _----=> need-resched
 #                || / _---=> hardirq/softirq
 #                ||| / _--=> preempt-depth
 #                |||| /
 #                |||||     delay
 #  cmd     pid   ||||| time  |   caller
 #     \   /      |||||   \   |   /
    bash-4281    1d.s6  265us : update_max_tr_single: Failed to swap buffers due to commit in progress

Note the latency time and the functions that disabled the irqs or preemption
will still be listed.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

parent 659372d3

kernel/trace/trace.c

+12 −1

Original line number	Original line	Diff line number	Diff line
	@@ -482,9 +482,20 @@ update_max_tr_single(struct trace_array tr, struct task_struct tsk, int cpu)

	ret = ring_buffer_swap_cpu(max_tr.buffer, tr->buffer, cpu);		ret = ring_buffer_swap_cpu(max_tr.buffer, tr->buffer, cpu);

			if (ret == -EBUSY) {
			/*
			* We failed to swap the buffer due to a commit taking
			* place on this CPU. We fail to record, but we reset
			* the max trace buffer (no one writes directly to it)
			* and flag that it failed.
			*/
			trace_array_printk(&max_tr, _THIS_IP_,
			"Failed to swap buffers due to commit in progress\n");
			}

	ftrace_enable_cpu();		ftrace_enable_cpu();

	WARN_ON_ONCE(ret && ret != -EAGAIN);		WARN_ON_ONCE(ret && ret != -EAGAIN && ret != -EBUSY);

	__update_max_tr(tr, tsk, cpu);		__update_max_tr(tr, tsk, cpu);
	__raw_spin_unlock(&ftrace_max_lock);		__raw_spin_unlock(&ftrace_max_lock);

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