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linux/Documentation/trace
Steven Rostedt 94d529a325 ftrace: Document that multiple function_graph tracing may have different times
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)

Link: https://lore.kernel.org/all/20250114101806.b2778cb01f34f5be9d23ad98@kernel.org/

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Suggested-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/20250114101202.02e7bc68@gandalf.local.home
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2025-01-14 10:45:24 -05:00
..
coresight
postprocess
rv
boottime-trace.rst
debugging.rst
events-kmem.rst
events-msr.rst
events-nmi.rst
events-power.rst
events.rst
fprobe.rst
fprobetrace.rst
ftrace-design.rst
ftrace-uses.rst
ftrace.rst
function-graph-fold.vim
hisi-ptt.rst
histogram-design.rst
histogram.rst
hwlat_detector.rst
index.rst
intel_th.rst
kprobes.rst
kprobetrace.rst
mmiotrace.rst
osnoise-tracer.rst
ring-buffer-design.rst
ring-buffer-map.rst
stm.rst
sys-t.rst
timerlat-tracer.rst
tracepoint-analysis.rst
tracepoints.rst
uprobetracer.rst
user_events.rst