[RFC PATCH 1/2] ftrace: add quiet option to trace_irqsoff

[Mathieu Desnoyers]

Allow irqsoff and preemptoff tracers to be used by perf and lttng
without always having ftrace writing into its own ring buffers. Add this
"quiet" option to allow using those tracers without actively tracing
into the ftrace ring buffer.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
 kernel/trace/trace.h         |  1 +
 kernel/trace/trace_irqsoff.c | 19 +++++++++++++------
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 919d9d0..490413c 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -967,6 +967,7 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
 		C(STOP_ON_FREE,		"disable_on_free"),	\
 		C(IRQ_INFO,		"irq-info"),		\
 		C(MARKERS,		"markers"),		\
+		C(QUIET,		"quiet"),		\
 		FUNCTION_FLAGS					\
 		FGRAPH_FLAGS					\
 		STACK_FLAGS					\
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index e4e5658..4ed348a 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -67,6 +67,8 @@ static inline int irqsoff_display_graph(struct trace_array *tr, int set)
 # define is_graph(tr) false
 #endif
 
+#define is_quiet(tr)	((tr)->trace_flags & TRACE_ITER_QUIET)
+
 /*
  * Sequence count - we record it when starting a measurement and
  * skip the latency if the sequence has changed - some other section
@@ -321,9 +323,11 @@ check_critical_timing(struct trace_array *tr,
 	if (!report_latency(tr, delta))
 		goto out_unlock;
 
-	__trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
-	/* Skip 5 functions to get to the irq/preempt enable function */
-	__trace_stack(tr, flags, 5, pc);
+	if (!is_quiet(tr)) {
+		__trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
+		/* Skip 5 functions to get to the irq/preempt enable function */
+		__trace_stack(tr, flags, 5, pc);
+	}
 
 	if (data->critical_sequence != max_sequence)
 		goto out_unlock;
@@ -343,7 +347,8 @@ out_unlock:
 out:
 	data->critical_sequence = max_sequence;
 	data->preempt_timestamp = ftrace_now(cpu);
-	__trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
+	if (!is_quiet(tr))
+		__trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
 }
 
 static inline void
@@ -375,7 +380,8 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip)
 
 	local_save_flags(flags);
 
-	__trace_function(tr, ip, parent_ip, flags, preempt_count());
+	if (!is_quiet(tr))
+		__trace_function(tr, ip, parent_ip, flags, preempt_count());
 
 	per_cpu(tracing_cpu, cpu) = 1;
 
@@ -409,7 +415,8 @@ stop_critical_timing(unsigned long ip, unsigned long parent_ip)
 	atomic_inc(&data->disabled);
 
 	local_save_flags(flags);
-	__trace_function(tr, ip, parent_ip, flags, preempt_count());
+	if (!is_quiet(tr))
+		__trace_function(tr, ip, parent_ip, flags, preempt_count());
 	check_critical_timing(tr, data, parent_ip ? : ip, cpu);
 	data->critical_start = 0;
 	atomic_dec(&data->disabled);
-- 
2.1.4

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