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ring-buffer: only enable ring_buffer_swap_cpu when needed

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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>
This commit is contained in:
Steven Rostedt 2009-09-04 14:24:40 -04:00 committed by Steven Rostedt
parent 62f0b3eb5c
commit 85bac32c4a
3 changed files with 21 additions and 0 deletions
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9
include/linux/ring_buffer.h
View File

@ -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);

8
kernel/trace/Kconfig
View File

@ -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.

4
kernel/trace/ring_buffer.c
View File

@ -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