On Tue, 3 Jun 2014 21:12:49 +0400
Stanislav Fomichev <stfomic...@yandex-team.ru> wrote:
> Currently, tracing_thresh works only if we specify it before selecting
> function_graph tracer. If we do the opposite, tracing_thresh will change
> it's value, but it will not be applied.
> To fix it, we need to always register handlers which take tracing_thresh into
> account.
>
> Signed-off-by: Stanislav Fomichev <stfomic...@yandex-team.ru>
> ---
> kernel/trace/trace_functions_graph.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/trace/trace_functions_graph.c
> b/kernel/trace/trace_functions_graph.c
> index deff11200261..a894031986a3 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -433,12 +433,8 @@ static int graph_trace_init(struct trace_array *tr)
> int ret;
>
> set_graph_array(tr);
> - if (tracing_thresh)
> - ret = register_ftrace_graph(&trace_graph_thresh_return,
> - &trace_graph_thresh_entry);
> - else
> - ret = register_ftrace_graph(&trace_graph_return,
> - &trace_graph_entry);
> + ret = register_ftrace_graph(&trace_graph_thresh_return,
> + &trace_graph_thresh_entry);
> if (ret)
> return ret;
> tracing_start_cmdline_record();
I would rather not endure the overhead of checking tracing_thresh
every time. I never use it, I didn't even know there was someone that
did ;-)
I'm not saying you can't fix this bug, I'm just saying that it
shouldn't be done this way.
Ideally there should be a callback for the tracer to deal with it, but
instead, you can for now just hardcode a function graph tracer callback
into tracing_max_lat_write(). Something like this:
if (ptr == &tracing_thresh)
ftrace_update_func_graph_thresh();
And then if the function tracer is active, stop it, and then restart it
with the tracing thresh function.
-- Steve
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