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@@ -429,24 +429,28 @@ config PROBE_EVENTS
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def_bool n
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config DYNAMIC_FTRACE
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- bool "enable/disable ftrace tracepoints dynamically"
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+ bool "enable/disable function tracing dynamically"
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depends on FUNCTION_TRACER
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depends on HAVE_DYNAMIC_FTRACE
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default y
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help
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- This option will modify all the calls to ftrace dynamically
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- (will patch them out of the binary image and replace them
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- with a No-Op instruction) as they are called. A table is
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- created to dynamically enable them again.
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+ This option will modify all the calls to function tracing
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+ dynamically (will patch them out of the binary image and
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+ replace them with a No-Op instruction) on boot up. During
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+ compile time, a table is made of all the locations that ftrace
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+ can function trace, and this table is linked into the kernel
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+ image. When this is enabled, functions can be individually
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+ enabled, and the functions not enabled will not affect
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+ performance of the system.
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+
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+ See the files in /sys/kernel/debug/tracing:
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+ available_filter_functions
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+ set_ftrace_filter
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+ set_ftrace_notrace
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This way a CONFIG_FUNCTION_TRACER kernel is slightly larger, but
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otherwise has native performance as long as no tracing is active.
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- The changes to the code are done by a kernel thread that
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- wakes up once a second and checks to see if any ftrace calls
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- were made. If so, it runs stop_machine (stops all CPUS)
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- and modifies the code to jump over the call to ftrace.
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-
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config DYNAMIC_FTRACE_WITH_REGS
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def_bool y
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depends on DYNAMIC_FTRACE
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Ingo Molnar