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authorSteven Rostedt <srostedt@redhat.com>2009-09-04 22:24:40 +0400
committerSteven Rostedt <rostedt@goodmis.org>2009-09-05 03:42:22 +0400
commit85bac32c4a52c592b857f2c360cc5ec93a097d70 (patch)
tree510e516dd5fa388cb9582a2f6b055f3725fbf2c1
parent62f0b3eb5cb58931a02ee4e599e19c80a171e351 (diff)
downloadlinux-85bac32c4a52c592b857f2c360cc5ec93a097d70.tar.xz
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: Steven Rostedt <rostedt@goodmis.org>
-rw-r--r--include/linux/ring_buffer.h9
-rw-r--r--kernel/trace/Kconfig8
-rw-r--r--kernel/trace/ring_buffer.c4
3 files changed, 21 insertions, 0 deletions
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index e061b4ecdc3a..5fcc31ed5771 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -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);
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 163fbfc2f39f..1ea0d1234f4a 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -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.
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 1766c0e8db5a..454e74e718cf 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -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 @@ out:
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