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Commit 85bac32c authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
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ring-buffer: only enable ring_buffer_swap_cpu when needed 



Since the ability to swap the cpu buffers adds a small overhead to
the recording of a trace, we only want to add it when needed.

Only the irqsoff and preemptoff tracers use this feature, and both are
not recommended for production kernels. This patch disables its use
when neither irqsoff nor preemptoff is configured.

Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 62f0b3eb

include/linux/ring_buffer.h

+9 −0
Original line number Diff line number Diff line
@@ -140,8 +140,17 @@ unsigned long ring_buffer_size(struct ring_buffer *buffer); 
void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu);

void ring_buffer_reset(struct ring_buffer *buffer);



#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP

int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,

			 struct ring_buffer *buffer_b, int cpu);

#else

static inline int

ring_buffer_swap_cpu(struct ring_buffer *buffer_a,

		     struct ring_buffer *buffer_b, int cpu)

{

	return -ENODEV;

}

#endif



int ring_buffer_empty(struct ring_buffer *buffer);

int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu);

kernel/trace/Kconfig

+8 −0
Original line number Diff line number Diff line
@@ -62,6 +62,12 @@ config EVENT_TRACING 
config CONTEXT_SWITCH_TRACER

	bool



config RING_BUFFER_ALLOW_SWAP

	bool

	help

	 Allow the use of ring_buffer_swap_cpu.

	 Adds a very slight overhead to tracing when enabled.



# All tracer options should select GENERIC_TRACER. For those options that are

# enabled by all tracers (context switch and event tracer) they select TRACING.

# This allows those options to appear when no other tracer is selected. But the
@@ -146,6 +152,7 @@ config IRQSOFF_TRACER 
	select TRACE_IRQFLAGS

	select GENERIC_TRACER

	select TRACER_MAX_TRACE

	select RING_BUFFER_ALLOW_SWAP

	help

	  This option measures the time spent in irqs-off critical

	  sections, with microsecond accuracy.
@@ -167,6 +174,7 @@ config PREEMPT_TRACER 
	depends on PREEMPT

	select GENERIC_TRACER

	select TRACER_MAX_TRACE

	select RING_BUFFER_ALLOW_SWAP

	help

	  This option measures the time spent in preemption off critical

	  sections, with microsecond accuracy.

kernel/trace/ring_buffer.c

+4 −0
Original line number Diff line number Diff line
@@ -2084,6 +2084,7 @@ rb_reserve_next_event(struct ring_buffer *buffer, 


	rb_start_commit(cpu_buffer);



#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP

	/*

	 * Due to the ability to swap a cpu buffer from a buffer

	 * it is possible it was swapped before we committed.
@@ -2096,6 +2097,7 @@ rb_reserve_next_event(struct ring_buffer *buffer, 
		local_dec(&cpu_buffer->commits);

		return NULL;

	}

#endif



	length = rb_calculate_event_length(length);

 again:
@@ -3498,6 +3500,7 @@ int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu) 
}

EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);



#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP

/**

 * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers

 * @buffer_a: One buffer to swap with
@@ -3573,6 +3576,7 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a, 
	return ret;

}

EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);

#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */



/**

 * ring_buffer_alloc_read_page - allocate a page to read from buffer