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Message-ID: <20140604154149.3c2857dc@gandalf.local.home>
Date: Wed, 4 Jun 2014 15:41:49 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Stanislav Fomichev <stfomichev@...dex-team.ru>
Cc: fweisbec@...il.com, mingo@...hat.com, jovi.zhangwei@...wei.com,
namhyung.kim@....com, tom.zanussi@...ux.intel.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] tracing: let user specify tracing_thresh after
selecting function_graph
On Wed, 4 Jun 2014 17:33:50 +0400
Stanislav Fomichev <stfomichev@...dex-team.ru> wrote:
> > 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.
> Attached new patch which adds new callback and uses it in function_graph
> tracer (not sure whether I need to check graph_array in
> graph_trace_update_thresh). Maybe it makes sense to split it into two commits
> (add callback itself, use it in the function_graph tracer)?
Sometimes it's better to do it in two commits, but as this is rather
a small change, one is good enough.
>
> Btw, I also tried to use static_keys/jump_labels in places where
> tracing_thresh is checked, but got double faults. Is there a reason I
> can't use jump labels inside tracers?
You mean inside the function tracers. I could envision problems with
that, but I don't know exactly what would cause those problems. Have
patches to show? You may have done something unrelated that caused the
issue.
>
> ---
>
> 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 add update_thresh callback which is called whenever
> tracing_thresh is updated and for function_graph tracer we register
> handler which reinitializes tracer depending on tracing_thresh.
>
> Signed-off-by: Stanislav Fomichev <stfomichev@...dex-team.ru>
> ---
> kernel/trace/trace.c | 60 +++++++++++++++++++++++++++++++-----
> kernel/trace/trace.h | 2 ++
> kernel/trace/trace_functions_graph.c | 10 ++++++
> 3 files changed, 65 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 737b0efa1a62..06fbb4b7e646 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -4077,10 +4077,9 @@ tracing_set_trace_write(struct file *filp, const char __user *ubuf,
> }
>
> static ssize_t
> -tracing_max_lat_read(struct file *filp, char __user *ubuf,
> - size_t cnt, loff_t *ppos)
> +nsecs_read(unsigned long *ptr, char __user *ubuf,
Nit, although these are static functions, I still like to add "trace"
or "tracing" to their names. Makes it easier to grep for.
> + size_t cnt, loff_t *ppos)
> {
> - unsigned long *ptr = filp->private_data;
> char buf[64];
> int r;
>
> @@ -4092,10 +4091,9 @@ tracing_max_lat_read(struct file *filp, char __user *ubuf,
> }
>
> static ssize_t
> -tracing_max_lat_write(struct file *filp, const char __user *ubuf,
> - size_t cnt, loff_t *ppos)
> +nsecs_write(unsigned long *ptr, const char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> {
> - unsigned long *ptr = filp->private_data;
> unsigned long val;
> int ret;
>
> @@ -4108,6 +4106,47 @@ tracing_max_lat_write(struct file *filp, const char __user *ubuf,
> return cnt;
> }
>
> +static ssize_t
> +tracing_thresh_read(struct file *filp, char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> +{
> + return nsecs_read(&tracing_thresh, ubuf, cnt, ppos);
> +}
> +
> +static ssize_t
> +tracing_thresh_write(struct file *filp, const char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> +{
> + struct trace_array *tr = filp->private_data;
> + int ret;
> +
> + ret = nsecs_write(&tracing_thresh, ubuf, cnt, ppos);
> + if (ret < 0)
> + return ret;
> +
You need to take the trace_types_lock mutex here, otherwise
current_trace can change from under you.
-- Steve
> + if (tr->current_trace->update_thresh) {
> + ret = tr->current_trace->update_thresh(tr);
> + if (ret)
> + return ret;
> + }
> +
> + return cnt;
> +}
> +
> +static ssize_t
> +tracing_max_lat_read(struct file *filp, char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> +{
> + return nsecs_read(filp->private_data, ubuf, cnt, ppos);
> +}
> +
> +static ssize_t
> +tracing_max_lat_write(struct file *filp, const char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> +{
> + return nsecs_write(filp->private_data, ubuf, cnt, ppos);
> +}
> +
> static int tracing_open_pipe(struct inode *inode, struct file *filp)
> {
> struct trace_array *tr = inode->i_private;
> @@ -5024,6 +5063,13 @@ static int snapshot_raw_open(struct inode *inode, struct file *filp)
> #endif /* CONFIG_TRACER_SNAPSHOT */
>
>
> +static const struct file_operations tracing_thresh_fops = {
> + .open = tracing_open_generic,
> + .read = tracing_thresh_read,
> + .write = tracing_thresh_write,
> + .llseek = generic_file_llseek,
> +};
> +
> static const struct file_operations tracing_max_lat_fops = {
> .open = tracing_open_generic,
> .read = tracing_max_lat_read,
> @@ -6359,7 +6405,7 @@ static __init int tracer_init_debugfs(void)
> #endif
>
> trace_create_file("tracing_thresh", 0644, d_tracer,
> - &tracing_thresh, &tracing_max_lat_fops);
> + &global_trace, &tracing_thresh_fops);
>
> trace_create_file("README", 0444, d_tracer,
> NULL, &tracing_readme_fops);
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 2e29d7ba5a52..960c523de47d 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -321,6 +321,7 @@ struct tracer_flags {
> * @reset: called when one switches to another tracer
> * @start: called when tracing is unpaused (echo 1 > tracing_enabled)
> * @stop: called when tracing is paused (echo 0 > tracing_enabled)
> + * @update_thresh: called when tracing_thresh is updated
> * @open: called when the trace file is opened
> * @pipe_open: called when the trace_pipe file is opened
> * @wait_pipe: override how the user waits for traces on trace_pipe
> @@ -340,6 +341,7 @@ struct tracer {
> void (*reset)(struct trace_array *tr);
> void (*start)(struct trace_array *tr);
> void (*stop)(struct trace_array *tr);
> + int (*update_thresh)(struct trace_array *tr);
> void (*open)(struct trace_iterator *iter);
> void (*pipe_open)(struct trace_iterator *iter);
> void (*wait_pipe)(struct trace_iterator *iter);
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index deff11200261..7440541a3b4f 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -450,6 +450,15 @@ static void graph_trace_reset(struct trace_array *tr)
> {
> tracing_stop_cmdline_record();
> unregister_ftrace_graph();
> + set_graph_array(NULL);
Hmm, this looks like it can cause issues. Unless you change
trace_graph_entry() and trace_graph_return to have:
struct trace_array *tr = ACCESS_ONCE(graph_array);
[..]
if (!tr)
return 0;
-- Steve
> +}
> +
> +void graph_trace_update_thresh(struct trace_array *tr)
> +{
> + if (graph_array) {
> + graph_trace_reset(tr);
> + graph_trace_init(tr);
> + }
> }
>
> static int max_bytes_for_cpu;
> @@ -1501,6 +1510,7 @@ static struct trace_event graph_trace_ret_event = {
>
> static struct tracer graph_trace __tracer_data = {
> .name = "function_graph",
> + .update_thresh = graph_trace_update_thresh,
> .open = graph_trace_open,
> .pipe_open = graph_trace_open,
> .close = graph_trace_close,
--
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