tracing/function-return-tracer: set a more human readable output
Impact: feature
This patch sets a C-like output for the function graph tracing.
For this aim, we now call two handler for each function: one on the entry
and one other on return. This way we can draw a well-ordered call stack.
The pid of the previous trace is loosely stored to be compared against
the one of the current trace to see if there were a context switch.
Without this little feature, the call tree would seem broken at
some locations.
We could use the sched_tracer to capture these sched_events but this
way of processing is much more simpler.
2 spaces have been chosen for indentation to fit the screen while deep
calls. The time of execution in nanosecs is printed just after closed
braces, it seems more easy this way to find the corresponding function.
If the time was printed as a first column, it would be not so easy to
find the corresponding function if it is called on a deep depth.
I plan to output the return value but on 32 bits CPU, the return value
can be 32 or 64, and its difficult to guess on which case we are.
I don't know what would be the better solution on X86-32: only print
eax (low-part) or even edx (high-part).
Actually it's thee same problem when a function return a 8 bits value, the
high part of eax could contain junk values...
Here is an example of trace:
sys_read() {
fget_light() {
} 526
vfs_read() {
rw_verify_area() {
security_file_permission() {
cap_file_permission() {
} 519
} 1564
} 2640
do_sync_read() {
pipe_read() {
__might_sleep() {
} 511
pipe_wait() {
prepare_to_wait() {
} 760
deactivate_task() {
dequeue_task() {
dequeue_task_fair() {
dequeue_entity() {
update_curr() {
update_min_vruntime() {
} 504
} 1587
clear_buddies() {
} 512
add_cfs_task_weight() {
} 519
update_min_vruntime() {
} 511
} 5602
dequeue_entity() {
update_curr() {
update_min_vruntime() {
} 496
} 1631
clear_buddies() {
} 496
update_min_vruntime() {
} 527
} 4580
hrtick_update() {
hrtick_start_fair() {
} 488
} 1489
} 13700
} 14949
} 16016
msecs_to_jiffies() {
} 496
put_prev_task_fair() {
} 504
pick_next_task_fair() {
} 489
pick_next_task_rt() {
} 496
pick_next_task_fair() {
} 489
pick_next_task_idle() {
} 489
------------8<---------- thread 4 ------------8<----------
finish_task_switch() {
} 1203
do_softirq() {
__do_softirq() {
__local_bh_disable() {
} 669
rcu_process_callbacks() {
__rcu_process_callbacks() {
cpu_quiet() {
rcu_start_batch() {
} 503
} 1647
} 3128
__rcu_process_callbacks() {
} 542
} 5362
_local_bh_enable() {
} 587
} 8880
} 9986
kthread_should_stop() {
} 669
deactivate_task() {
dequeue_task() {
dequeue_task_fair() {
dequeue_entity() {
update_curr() {
calc_delta_mine() {
} 511
update_min_vruntime() {
} 511
} 2813
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 9e19976..7e2d3b9 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1498,12 +1498,13 @@
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
-static atomic_t ftrace_retfunc_active;
+static atomic_t ftrace_graph_active;
-/* The callback that hooks the return of a function */
-trace_function_graph_t ftrace_graph_function =
- (trace_function_graph_t)ftrace_stub;
-
+/* The callbacks that hook a function */
+trace_func_graph_ret_t ftrace_graph_return =
+ (trace_func_graph_ret_t)ftrace_stub;
+trace_func_graph_ent_t ftrace_graph_entry =
+ (trace_func_graph_ent_t)ftrace_stub;
/* Try to assign a return stack array on FTRACE_RETSTACK_ALLOC_SIZE tasks. */
static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
@@ -1569,7 +1570,8 @@
return ret;
}
-int register_ftrace_graph(trace_function_graph_t func)
+int register_ftrace_graph(trace_func_graph_ret_t retfunc,
+ trace_func_graph_ent_t entryfunc)
{
int ret = 0;
@@ -1583,14 +1585,15 @@
ret = -EBUSY;
goto out;
}
- atomic_inc(&ftrace_retfunc_active);
+ atomic_inc(&ftrace_graph_active);
ret = start_graph_tracing();
if (ret) {
- atomic_dec(&ftrace_retfunc_active);
+ atomic_dec(&ftrace_graph_active);
goto out;
}
ftrace_tracing_type = FTRACE_TYPE_RETURN;
- ftrace_graph_function = func;
+ ftrace_graph_return = retfunc;
+ ftrace_graph_entry = entryfunc;
ftrace_startup();
out:
@@ -1602,8 +1605,9 @@
{
mutex_lock(&ftrace_sysctl_lock);
- atomic_dec(&ftrace_retfunc_active);
- ftrace_graph_function = (trace_function_graph_t)ftrace_stub;
+ atomic_dec(&ftrace_graph_active);
+ ftrace_graph_return = (trace_func_graph_ret_t)ftrace_stub;
+ ftrace_graph_entry = (trace_func_graph_ent_t)ftrace_stub;
ftrace_shutdown();
/* Restore normal tracing type */
ftrace_tracing_type = FTRACE_TYPE_ENTER;
@@ -1614,7 +1618,7 @@
/* Allocate a return stack for newly created task */
void ftrace_graph_init_task(struct task_struct *t)
{
- if (atomic_read(&ftrace_retfunc_active)) {
+ if (atomic_read(&ftrace_graph_active)) {
t->ret_stack = kmalloc(FTRACE_RETFUNC_DEPTH
* sizeof(struct ftrace_ret_stack),
GFP_KERNEL);
@@ -1638,5 +1642,3 @@
}
#endif
-
-