From: "Steven Rostedt (VMware)" <rost...@goodmis.org> If a ftrace callback requires "rcu_is_watching", then it adds the FTRACE_OPS_FL_RCU flag and it will not be called if RCU is not "watching". But this means that it will use a trampoline when called, and this slows down the function tracing a tad. By checking rcu_is_watching() from within the callback, it no longer needs the RCU flag set in the ftrace_ops and it can be safely called directly.
Link: https://lkml.kernel.org/r/20201028115613.591878...@goodmis.org Link: https://lkml.kernel.org/r/20201106023547.711035...@goodmis.org Cc: Peter Zijlstra <pet...@infradead.org> Cc: Ingo Molnar <mi...@kernel.org> Cc: Josh Poimboeuf <jpoim...@redhat.com> Cc: Jiri Kosina <ji...@kernel.org> Cc: Miroslav Benes <mbe...@suse.cz> Cc: Petr Mladek <pmla...@suse.com> Cc: Masami Hiramatsu <mhira...@kernel.org> Cc: Andrew Morton <a...@linux-foundation.org> Cc: Jiri Olsa <jo...@redhat.com> Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org> --- kernel/trace/trace_event_perf.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c index fd58d83861d8..a2b9fddb8148 100644 --- a/kernel/trace/trace_event_perf.c +++ b/kernel/trace/trace_event_perf.c @@ -441,6 +441,9 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip, int rctx; int bit; + if (!rcu_is_watching()) + return; + if ((unsigned long)ops->private != smp_processor_id()) return; @@ -484,7 +487,6 @@ static int perf_ftrace_function_register(struct perf_event *event) { struct ftrace_ops *ops = &event->ftrace_ops; - ops->flags = FTRACE_OPS_FL_RCU; ops->func = perf_ftrace_function_call; ops->private = (void *)(unsigned long)nr_cpu_ids; -- 2.28.0
