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

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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>
This commit is contained in:
Steven Rostedt 2009-09-03 19:13:05 -04:00 committed by Steven Rostedt
parent 659372d3e4
commit e8165dbb03
1 changed files with 12 additions and 1 deletions
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13
kernel/trace/trace.c
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@ -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);
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();
WARN_ON_ONCE(ret && ret != -EAGAIN);
WARN_ON_ONCE(ret && ret != -EAGAIN && ret != -EBUSY);
__update_max_tr(tr, tsk, cpu);
__raw_spin_unlock(&ftrace_max_lock);