Linus, A regression showed up that there's a large delay when enabling all events. This was prevalent when FTRACE_SELFTEST was enabled which enables all events several times, and caused the system bootup to pause for over a minute.
This was tracked down to an addition of a synchronize_sched() performed when system call tracepoints are unregistered. The synchronize_sched() is needed between the unregistering of the system call tracepoint and a deletion of a tracing instance buffer. But placing the synchronize_sched() in the unreg of *every* system call tracepoint is a bit overboard. A single synchronize_sched() before the deletion of the instance is sufficient. Please pull the latest trace-fixes-3.13-rc2 tree, which can be found at: git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git trace-fixes-3.13-rc2 Tag SHA1: c1bd293f5ee07cf4426e54f8124dd3eb2bff450a Head SHA1: 3ccb01239201af06a07482ec686b14cd148102a5 Steven Rostedt (1): tracing: Only run synchronize_sched() at instance deletion time ---- kernel/trace/trace_events.c | 3 +++ kernel/trace/trace_syscalls.c | 10 ---------- 2 files changed, 3 insertions(+), 10 deletions(-) --------------------------- commit 3ccb01239201af06a07482ec686b14cd148102a5 Author: Steven Rostedt <rost...@goodmis.org> Date: Tue Dec 3 12:41:20 2013 -0500 tracing: Only run synchronize_sched() at instance deletion time It has been reported that boot up with FTRACE_SELFTEST enabled can take a very long time. There can be stalls of over a minute. This was tracked down to the synchronize_sched() called when a system call event is disabled. As the self tests enable and disable thousands of events, this makes the synchronize_sched() get called thousands of times. The synchornize_sched() was added with d562aff93bfb53 "tracing: Add support for SOFT_DISABLE to syscall events" which caused this regression (added in 3.13-rc1). The synchronize_sched() is to protect against the events being accessed when a tracer instance is being deleted. When an instance is being deleted all the events associated to it are unregistered. The synchronize_sched() makes sure that no more users are running when it finishes. Instead of calling synchronize_sched() for all syscall events, we only need to call it once, after the events are unregistered and before the instance is deleted. The event_mutex is held during this action to prevent new users from enabling events. Link: http://lkml.kernel.org/r/20131203124120.427b9...@gandalf.local.home Reported-by: Petr Mladek <pmla...@suse.cz> Acked-by: Tom Zanussi <tom.zanu...@linux.intel.com> Acked-by: Petr Mladek <pmla...@suse.cz> Tested-by: Petr Mladek <pmla...@suse.cz> Signed-off-by: Steven Rostedt <rost...@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) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/