> 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)?
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?
---
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 <stfomic...@yandex-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,
+ 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;
+
+ 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);
+}
+
+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,
--
1.8.3.2
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