trace: set max latency variable to zero on default (1092307d) · Commits · 戴 / test

Impact: trace max latencies on start of latency tracing This patch sets the max latency to zero whenever one of the irq variant tracers or the wakeup tracer is set to current tracer. Most developers expect to see output when starting up a latency tracer. But since the max_latency is already set to max, and it takes a latency greater than max_latency to be recorded, there is no trace. This is not the expected behavior and has even confused myself. Signed-off-by:

Steven Rostedt <srostedt@redhat.com> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

kernel/trace/trace.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -40,7 +40,7 @@

		#define TRACE_BUFFER_FLAGS (RB_FL_OVERWRITE)

		unsigned long __read_mostly tracing_max_latency = (cycle_t)ULONG_MAX;
		unsigned long __read_mostly tracing_max_latency;
		unsigned long __read_mostly tracing_thresh;

		/*

kernel/trace/trace_irqsoff.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -380,6 +380,7 @@ static void stop_irqsoff_tracer(struct trace_array *tr)

		static void __irqsoff_tracer_init(struct trace_array *tr)
		{
		tracing_max_latency = 0;
		irqsoff_trace = tr;
		/* make sure that the tracer is visible */
		smp_wmb();

kernel/trace/trace_sched_wakeup.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -333,6 +333,7 @@ static void stop_wakeup_tracer(struct trace_array *tr)

		static int wakeup_tracer_init(struct trace_array *tr)
		{
		tracing_max_latency = 0;
		wakeup_trace = tr;
		start_wakeup_tracer(tr);
		return 0;

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