Messages in this thread Patch in this message | | | Date | Fri, 30 Oct 2020 17:31:51 -0400 | From | Steven Rostedt <> | Subject | [PATCH 09/11 v2] perf/ftrace: Check for rcu_is_watching() in callback function |
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From: "Steven Rostedt (VMware)" <rostedt@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/20201028115613.591878956@goodmis.org
Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jiri Olsa <jolsa@redhat.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@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
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