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>

1 files changed, 8 insertions, 0 deletions

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.