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Date: Thu, 17 Jul 2014 14:08:51 -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: [PATCHv3] tracing: let user specify tracing_thresh after
selecting function_graph
On Tue, 15 Jul 2014 19:31:57 +0400
Stanislav Fomichev <stfomichev@...dex-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 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 | 65 ++++++++++++++++++++++++++++++++----
> kernel/trace/trace.h | 2 ++
> kernel/trace/trace_functions_graph.c | 20 +++++++++--
> 3 files changed, 77 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index f243444a3772..986e6cad27d7 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -4224,10 +4224,9 @@ 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)
> +tracing_nsecs_read(unsigned long *ptr, char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> {
> - unsigned long *ptr = filp->private_data;
> char buf[64];
> int r;
>
> @@ -4239,10 +4238,9 @@ 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)
> +tracing_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;
>
> @@ -4255,6 +4253,52 @@ 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 tracing_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;
> +
> + mutex_lock(&trace_types_lock);
> + ret = tracing_nsecs_write(&tracing_thresh, ubuf, cnt, ppos);
> + if (ret < 0)
> + goto out;
> +
> + if (tr->current_trace->update_thresh) {
> + ret = tr->current_trace->update_thresh(tr);
> + if (ret < 0)
> + goto out;
> + }
> +
> + ret = cnt;
> +out:
> + mutex_unlock(&trace_types_lock);
> +
> + return ret;
> +}
> +
> +static ssize_t
> +tracing_max_lat_read(struct file *filp, char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> +{
> + return tracing_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 tracing_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;
> @@ -5156,6 +5200,13 @@ 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,
> @@ -6519,7 +6570,7 @@ static __init int tracer_init_debugfs(void)
> init_tracer_debugfs(&global_trace, d_tracer);
>
> 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 9258f5a815db..385391fb1d3b 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -339,6 +339,7 @@ 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
> * @close: called when the trace file is released
> @@ -357,6 +358,7 @@ 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 (*close)(struct trace_iterator *iter);
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 4de3e57f723c..10d86cf83cb8 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -279,7 +279,7 @@ static inline int ftrace_graph_ignore_irqs(void)
>
> int trace_graph_entry(struct ftrace_graph_ent *trace)
> {
> - struct trace_array *tr = graph_array;
> + struct trace_array *tr = ACCESS_ONCE(graph_array);
> struct trace_array_cpu *data;
> unsigned long flags;
> long disabled;
> @@ -287,7 +287,7 @@ int trace_graph_entry(struct ftrace_graph_ent *trace)
> int cpu;
> int pc;
>
> - if (!ftrace_trace_task(current))
> + if (!tr || !ftrace_trace_task(current))
> return 0;
>
> /* trace it when it is-nested-in or is a function enabled. */
> @@ -384,13 +384,16 @@ void __trace_graph_return(struct trace_array *tr,
>
> void trace_graph_return(struct ftrace_graph_ret *trace)
> {
> - struct trace_array *tr = graph_array;
> + struct trace_array *tr = ACCESS_ONCE(graph_array);
> struct trace_array_cpu *data;
> unsigned long flags;
> long disabled;
> int cpu;
> int pc;
>
> + if (!tr)
> + return;
> +
Let's not add branches into the fast path. This isn't needed. I'll
explain below.
> local_irq_save(flags);
> cpu = raw_smp_processor_id();
> data = per_cpu_ptr(tr->trace_buffer.data, cpu);
> @@ -443,6 +446,16 @@ static void graph_trace_reset(struct trace_array *tr)
> {
> tracing_stop_cmdline_record();
> unregister_ftrace_graph();
> + set_graph_array(NULL);
> +}
> +
> +int graph_trace_update_thresh(struct trace_array *tr)
The only way graph_trace_update_thresh() can be called is if the
current tracer happens to be the function graph tracer. Which means
that we are currently tracing and graph_array will be set. This will
not be called if function graph tracing is not set, because it is
called with the trace_types_lock mutex held.
Get rid of the graph_array tests and don't modify it. That is, just do
the reset and init unconditionally here.
-- Steve
> +{
> + if (graph_array) {
> + graph_trace_reset(tr);
> + return graph_trace_init(tr);
> + }
> + return 0;
> }
>
> static int max_bytes_for_cpu;
> @@ -1495,6 +1508,7 @@ 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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