@@ -1328,6 +1328,19 @@ Options for function_graph tracer:
only a closing curly bracket "}" is displayed for
the return of a function.
+ funcgraph-retval
+ When set, the return event will include the function and
+ its return value. Note that even if the function return
+ type is void, a return value will also be printed, you
+ should ignore it. This option is off by default.
+
+ graph_retval_hex
+ Depend on function-retval. When set, the function return
+ value will be printed in hexadecimal format. If this is not
+ set and the return value looks like an error code, it will
+ be printed in signed decimal format, else in hexadecimal
+ format. This option is off by default.
+
sleep-time
When running function graph tracer, to include
the time a task schedules out in its function.
@@ -2673,6 +2686,48 @@ It is default disabled.
0) 1.757 us | } /* kmem_cache_free() */
0) 2.861 us | } /* putname() */
+The kernel function return value can be displayed. Note that even if the
+function return type is void, the return value is will still be printed.
+However you should ignore it. You can use this feature to locate kernel
+functions those return errors.
+
+ - hide: echo nofuncgraph-retval > trace_options
+ - show: echo funcgraph-retval > trace_options
+
+ Example with funcgraph-retval::
+
+ 1) | cgroup_migrate() {
+ 1) 0.651 us | cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */
+ 1) | cgroup_migrate_execute() {
+ 1) | cpu_cgroup_can_attach() {
+ 1) | cgroup_taskset_first() {
+ 1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */
+ 1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */
+ 1) 0.380 us | sched_rt_can_attach(); /* = 0x0 */
+ 1) 2.335 us | } /* cpu_cgroup_can_attach = -22 */
+ 1) 4.369 us | } /* cgroup_migrate_execute = -22 */
+ 1) 7.143 us | } /* cgroup_migrate = -22 */
+
+By default, if the return value looks like an error code, it will be printed in
+signed decimal format. In other cases, it will be printed in hexadecimal format.
+
+ - hexadecimal or signed decimal (default): echo nograph_retval_hex > trace_options
+ - hexadecimal: echo graph_retval_hex > trace_options
+
+ Example with graph_retval_hex::
+
+ 1) | cgroup_migrate() {
+ 1) 0.651 us | cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */
+ 1) | cgroup_migrate_execute() {
+ 1) | cpu_cgroup_can_attach() {
+ 1) | cgroup_taskset_first() {
+ 1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */
+ 1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */
+ 1) 0.380 us | sched_rt_can_attach(); /* = 0x0 */
+ 1) 2.335 us | } /* cpu_cgroup_can_attach = 0xffffffea */
+ 1) 4.369 us | } /* cgroup_migrate_execute = 0xffffffea */
+ 1) 7.143 us | } /* cgroup_migrate = 0xffffffea */
+
You can put some comments on specific functions by using
trace_printk() For example, if you want to put a comment inside
the __might_sleep() function, you just have to include
Add documentation for the two newly introduced options for the function_graph tracer. The new option funcgraph-retval is used to control whether or not to display the return value. The new option graph_retval_hex is used to control the display format of the return value. Signed-off-by: Donglin Peng <pengdonglin@sangfor.com.cn> --- Documentation/trace/ftrace.rst | 55 ++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+)