[PATCH 2/3] ftrace: add ftrace-buffer option

Mathieu Desnoyers
2015-11-02T22:43:23Z

In order to use ftrace tracers to generate tracepoints without doing
tracing to its own hardcoded ring buffers, add a ftrace-buffer option
(default: 1). When set to 0, it disables tracing into the ftrace
hardcoded buffers.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@redhat.com>
CC: Peter Zijlstra <peterz@infradead.org>
---
kernel/trace/trace.c | 4 +++-
kernel/trace/trace.h | 1 +
kernel/trace/trace_irqsoff.c | 19 +++++++++++--------
3 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6e79408..d664f0e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -472,7 +472,8 @@ static inline void trace_access_lock_init(void)
unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO | TRACE_ITER_SLEEP_TIME |
TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE |
- TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION;
+ TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION |
+ TRACE_ITER_FTRACE_BUFFER;

static void tracer_tracing_on(struct trace_array *tr)
{
@@ -862,6 +863,7 @@ static const char *trace_options[] = {
"irq-info",
"markers",
"function-trace",
+ "ftrace-buffer",
NULL
};

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 74bde81..29968e1 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -930,6 +930,7 @@ enum trace_iterator_flags {
TRACE_ITER_IRQ_INFO = 0x800000,
TRACE_ITER_MARKERS = 0x1000000,
TRACE_ITER_FUNCTION = 0x2000000,
+ TRACE_ITER_FTRACE_BUFFER = 0x4000000,
};

/*
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 8523ea3..3e5635d 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -334,9 +334,11 @@ 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 (trace_flags & TRACE_ITER_FTRACE_BUFFER) {
+ __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;
@@ -356,7 +358,8 @@ out_unlock:
out:
data->critical_sequence = max_sequence;
data->preempt_timestamp = ftrace_now(cpu);
- __trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
+ if (trace_flags & TRACE_ITER_FTRACE_BUFFER)
+ __trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
}

static inline void
@@ -387,9 +390,8 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip)
data->critical_start = parent_ip ? : ip;

local_save_flags(flags);
-
- __trace_function(tr, ip, parent_ip, flags, preempt_count());
-
+ if (trace_flags & TRACE_ITER_FTRACE_BUFFER)
+ __trace_function(tr, ip, parent_ip, flags, preempt_count());
per_cpu(tracing_cpu, cpu) = 1;

atomic_dec(&data->disabled);
@@ -422,7 +424,8 @@ 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 (trace_flags & TRACE_ITER_FTRACE_BUFFER)
+ __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