Re: [PATCH 2/2] nohz: Add basic tracing

[Steven Rostedt]

On Tue, 2013-04-23 at 18:12 +0000, Christoph Lameter wrote:
> On Mon, 22 Apr 2013, Frederic Weisbecker wrote:
> 
> > It's not obvious to find out why the full dynticks subsystem
> > doesn't always stop the tick: whether this is due to kthreads,
> > posix timers, perf events, etc...
> >
> > These new tracepoints are here to help the user diagnose
> > the failures and test this feature.
> 
> Very good. This will help a lot.

You can also do:

cd /sys/kernel/debug/tracing
echo 1 > max_graph_depth
echo function_graph > current_tracer

And then run your code, and look to see what happens on the cpu in
question:

cat per_cpu/cpuX/trace

The "max_graph_depth" of one will make the function graph tracer just
trace the first function that enters the kernel. You'll be able to see
if the kernel did anything to your userspace application that wasn't
planned.

"max_graph_depth" was added in 3.9-rc1

-- Steve


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