| Message ID | 20250114101202.02e7bc68@gandalf.local.home (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 94d529a3255ce65496e932173d7f13e801170597 |
| Headers | show |
| Series | ftrace: Document that multiple function_graph tracing may have different times | expand |
On Tue, 14 Jan 2025 10:12:02 -0500 Steven Rostedt <rostedt@goodmis.org> wrote: > From: Steven Rostedt <rostedt@goodmis.org> > > The function graph tracer now calculates the calltime internally and for > each instance. If there are two instances that are running function graph > tracer and are tracing the same functions, the timings of the length of > those functions may be slightly different: > > # trace-cmd record -B foo -p function_graph -B bar -p function_graph sleep 5 > # trace-cmd report > [..] > bar: sleep-981 [000] ...1. 1101.109027: funcgraph_entry: 0.764 us | mutex_unlock(); (ret=0xffff8abcc256c300) > foo: sleep-981 [000] ...1. 1101.109028: funcgraph_entry: 0.748 us | mutex_unlock(); (ret=0xffff8abcc256c300) > bar: sleep-981 [000] ..... 1101.109029: funcgraph_exit: 2.456 us | } (ret=0xffff8abcc256c300) > foo: sleep-981 [000] ..... 1101.109029: funcgraph_exit: 2.403 us | } (ret=0xffff8abcc256c300) > bar: sleep-981 [000] d..1. 1101.109031: funcgraph_entry: 0.844 us | fpregs_assert_state_consistent(); (ret=0x0) > foo: sleep-981 [000] d..1. 1101.109032: funcgraph_entry: 0.803 us | fpregs_assert_state_consistent(); (ret=0x0) > I added: Link: https://lore.kernel.org/all/20250114101806.b2778cb01f34f5be9d23ad98@kernel.org/ Suggested-by: Masami Hiramatsu <mhiramat@kernel.org> To this as well. -- Steve > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> > --- > Documentation/trace/ftrace.rst | 6 ++++++ > 1 file changed, 6 insertions(+)
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index 272464bb7c60..2b74f96d09d5 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -810,6 +810,12 @@ Here is the list of current tracers that may be configured. to draw a graph of function calls similar to C code source. + Note that the function graph calculates the timings of when the + function starts and returns internally and for each instance. If + there are two instances that run function graph tracer and traces + the same functions, the length of the timings may be slightly off as + each read the timestamp separately and not at the same time. + "blk" The block tracer. The tracer used by the blktrace user