Messages in this thread |  | | Subject | Re: [BUG] ftrace: support for SOFT_DISABLE to syscall events caused huge slowdown of ftrace startup test | From | Petr Mladek <> | Date | Wed, 04 Dec 2013 13:47:10 +0100 |
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Steven Rostedt píše v Út 03. 12. 2013 v 12:41 -0500: > On Tue, 03 Dec 2013 18:16:09 +0100 > Petr Mladek <pmladek@suse.cz> wrote: > > > Hi, > > > > I tested my ftrace-related patches and enabled also the startup test: > > > > CONFIG_FTRACE_SELFTEST=y > > CONFIG_FTRACE_STARTUP_TEST=y > > > > On today's kernel/git/tip/tip.git, the boot "freezed" for 1 minute when > > doing "Testing event system syscalls". > > > > A bisect pointed finger to the commit d562aff93bfb530b099 (tracing: Add > > support for SOFT_DISABLE to syscall events). > > > > It seems that the culprit are the "synchronize_sched" calls added to > > "unreg_event_syscall_enter" and "unreg_event_syscall_exit" functions. > > They are called 2312 times during the boot here and are responsible for > > the delay. > > > > I wonder if it might cause slowdown also at runtime. > > > > I am going to look deeper into the code and eventually come up with a > > solution. But it might take some time. I am still newbie in the kernel > > development. Any hints or tips are welcome ;-) > > > > Yeah, the synchronize_sched() at all disabling of syscall events seems > rather extreme. Perhaps this is good enough. > > Dose this work for you?
I could confirm that it removes the delay and looks fine to me.
Acked-by: Petr Mladek <pmladek@suse.cz>
> Tom, do you see anything wrong with this. I'm assuming that the > synchronize_sched() within the event unregistering, was there for > deleting of trace instances. By placing the synchronize_sched() only > within the deletion code, this should be good enough. > > -- Steve > > Signed-off-by: Steven Rostedt <rostedt@goodmis.org> > > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c > index f919a2e..a11800a 100644 > --- a/kernel/trace/trace_events.c > +++ b/kernel/trace/trace_events.c > @@ -2314,6 +2314,9 @@ int event_trace_del_tracer(struct trace_array *tr) > /* Disable any running events */ > __ftrace_set_clr_event_nolock(tr, NULL, NULL, NULL, 0); > > + /* Access to events are within rcu_read_lock_sched() */ > + synchronize_sched(); > + > down_write(&trace_event_sem); > __trace_remove_event_dirs(tr); > debugfs_remove_recursive(tr->event_dir); > diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c > index e4b6d11..ea90eb5 100644 > --- a/kernel/trace/trace_syscalls.c > +++ b/kernel/trace/trace_syscalls.c > @@ -431,11 +431,6 @@ static void unreg_event_syscall_enter(struct ftrace_event_file *file, > if (!tr->sys_refcount_enter) > unregister_trace_sys_enter(ftrace_syscall_enter, tr); > mutex_unlock(&syscall_trace_lock); > - /* > - * Callers expect the event to be completely disabled on > - * return, so wait for current handlers to finish. > - */ > - synchronize_sched(); > } > > static int reg_event_syscall_exit(struct ftrace_event_file *file, > @@ -474,11 +469,6 @@ static void unreg_event_syscall_exit(struct ftrace_event_file *file, > if (!tr->sys_refcount_exit) > unregister_trace_sys_exit(ftrace_syscall_exit, tr); > mutex_unlock(&syscall_trace_lock); > - /* > - * Callers expect the event to be completely disabled on > - * return, so wait for current handlers to finish. > - */ > - synchronize_sched(); > } > > static int __init init_syscall_trace(struct ftrace_event_call *call)
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