Messages in this thread | | | Subject | Re: [RFC PATCH 1/2] ftrace: Introduce cmdline argument ftrace_disabled | From | Tiezhu Yang <> | Date | Mon, 21 Jun 2021 09:21:31 +0800 |
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On 06/19/2021 11:22 PM, Steven Rostedt wrote: > On Sat, 19 Jun 2021 14:29:19 +0800 > Tiezhu Yang <yangtiezhu@loongson.cn> wrote: > >> If set CONFIG_FUNCTION_TRACER=y, we can use the following command to >> disable ftrace after boot up: >> echo 0 > /proc/sys/kernel/ftrace_enabled > I'd love to just remove that. It's original purpose was to stop function > tracing when the latency tracers were active. That's now done via a tracefs > option. The "ftrace_enabled" really has no use anymore. > >> ftrace_disabled is much stronger than ftrace_enabled, introduce a new >> cmdline argument ftrace_disabled for user to control whether to disable >> ftrace when boot up. > "ftrace_disabled" is triggered when an anomaly is detected, and for the > safety of the system, ftrace shuts down. It was never meant to be a user > triggered event.
Thanks for your explanation.
> > You have no rationale for this change. What's the purpose of this?
The "System Benchmarks Index Score" of UnixBench under FUNCTION_TRACER is lower than !FUNCTION_TRACER, I want to use this new cmdline argument ftrace_disabled to test it, this is the original intention.
I see the following help info of "config FUNCTION_TRACER":
[If it's runtime disabled (the bootup default), then the overhead of the instructions is very small and not measurable even in micro-benchmarks.]
I am not quite understand the above description, could you tell me how to avoid the runtime performance overhead under FUNCTION_TRACER?
Thanks, Tiezhu
> > -- Steve > > >> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn> >> --- >> kernel/trace/ftrace.c | 8 ++++++++ >> 1 file changed, 8 insertions(+) >> >> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c >> index 72ef4dc..a015699 100644 >> --- a/kernel/trace/ftrace.c >> +++ b/kernel/trace/ftrace.c >> @@ -5517,6 +5517,14 @@ static char ftrace_filter_buf[FTRACE_FILTER_SIZE] __initdata; >> /* Used by function selftest to not test if filter is set */ >> bool ftrace_filter_param __initdata; >> >> +static int __init set_ftrace_disabled(char *str) >> +{ >> + pr_info("Set ftrace_disabled to disable ftrace\n"); >> + ftrace_disabled = 1; >> + return 1; >> +} >> +__setup("ftrace_disabled", set_ftrace_disabled); >> + >> static int __init set_ftrace_notrace(char *str) >> { >> ftrace_filter_param = true;
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