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Subject[PATCH 3/3] ftrace: add ability to only trace swapper tasks
From: Steven Rostedt <srostedt@redhat.com>

Impact: New feature

This patch lets the swapper tasks of all CPUS be filtered by the
set_ftrace_pid file.

If '0' is echoed into this file, then all the idle tasks (aka swapper)
is flagged to be traced. This affects all CPU idle tasks.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
kernel/trace/ftrace.c | 74 +++++++++++++++++++++++++++++++++++++++++-------
1 files changed, 63 insertions(+), 11 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 10b1d7c..eb57dc1 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -49,6 +49,7 @@ static int last_ftrace_enabled;

/* set when tracing only a pid */
struct pid *ftrace_pid_trace;
+static struct pid * const ftrace_swapper_pid = (struct pid *)1;

/* Quick disabling of function tracer. */
int function_trace_stop;
@@ -1678,7 +1679,9 @@ ftrace_pid_read(struct file *file, char __user *ubuf,
char buf[64];
int r;

- if (ftrace_pid_trace)
+ if (ftrace_pid_trace == ftrace_swapper_pid)
+ r = sprintf(buf, "swapper tasks\n");
+ else if (ftrace_pid_trace)
r = sprintf(buf, "%u\n", pid_nr(ftrace_pid_trace));
else
r = sprintf(buf, "no pid\n");
@@ -1686,19 +1689,43 @@ ftrace_pid_read(struct file *file, char __user *ubuf,
return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
}

-static void clear_ftrace_pid_task(struct pid **pid)
+static void clear_ftrace_swapper(void)
{
struct task_struct *p;
+ int cpu;

- do_each_pid_task(*pid, PIDTYPE_PID, p) {
+ get_online_cpus();
+ for_each_online_cpu(cpu) {
+ p = idle_task(cpu);
clear_tsk_trace_trace(p);
- } while_each_pid_task(*pid, PIDTYPE_PID, p);
- put_pid(*pid);
+ }
+ put_online_cpus();
+}

- *pid = NULL;
+static void set_ftrace_swapper(void)
+{
+ struct task_struct *p;
+ int cpu;
+
+ get_online_cpus();
+ for_each_online_cpu(cpu) {
+ p = idle_task(cpu);
+ set_tsk_trace_trace(p);
+ }
+ put_online_cpus();
}

-static void set_ftrace_pid_task(struct pid *pid)
+static void clear_ftrace_pid(struct pid *pid)
+{
+ struct task_struct *p;
+
+ do_each_pid_task(pid, PIDTYPE_PID, p) {
+ clear_tsk_trace_trace(p);
+ } while_each_pid_task(pid, PIDTYPE_PID, p);
+ put_pid(pid);
+}
+
+static void set_ftrace_pid(struct pid *pid)
{
struct task_struct *p;

@@ -1707,6 +1734,24 @@ static void set_ftrace_pid_task(struct pid *pid)
} while_each_pid_task(pid, PIDTYPE_PID, p);
}

+static void clear_ftrace_pid_task(struct pid **pid)
+{
+ if (*pid == ftrace_swapper_pid)
+ clear_ftrace_swapper();
+ else
+ clear_ftrace_pid(*pid);
+
+ *pid = NULL;
+}
+
+static void set_ftrace_pid_task(struct pid *pid)
+{
+ if (pid == ftrace_swapper_pid)
+ set_ftrace_swapper();
+ else
+ set_ftrace_pid(pid);
+}
+
static ssize_t
ftrace_pid_write(struct file *filp, const char __user *ubuf,
size_t cnt, loff_t *ppos)
@@ -1737,11 +1782,18 @@ ftrace_pid_write(struct file *filp, const char __user *ubuf,
clear_ftrace_pid_task(&ftrace_pid_trace);

} else {
- pid = find_get_pid(val);
+ /* swapper task is special */
+ if (!val) {
+ pid = ftrace_swapper_pid;
+ if (pid == ftrace_pid_trace)
+ goto out;
+ } else {
+ pid = find_get_pid(val);

- if (pid == ftrace_pid_trace) {
- put_pid(pid);
- goto out;
+ if (pid == ftrace_pid_trace) {
+ put_pid(pid);
+ goto out;
+ }
}

if (ftrace_pid_trace)
--
1.5.6.5
--


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