Messages in this thread Patch in this message | | | From | Donglin Peng <> | Subject | [PATCH v4 2/2] tracing: Add documentation for funcgraph-retval and graph_retval_hex | Date | Wed, 15 Mar 2023 06:39:11 -0700 |
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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(+)
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index b927fb2b94dc..8ebe8d0b8838 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -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 -- 2.25.1
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