diff options
Diffstat (limited to 'kernel/trace/Kconfig')
-rw-r--r-- | kernel/trace/Kconfig | 24 |
1 files changed, 14 insertions, 10 deletions
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 192473b22799..fc382d6e2765 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig | |||
@@ -414,24 +414,28 @@ config PROBE_EVENTS | |||
414 | def_bool n | 414 | def_bool n |
415 | 415 | ||
416 | config DYNAMIC_FTRACE | 416 | config DYNAMIC_FTRACE |
417 | bool "enable/disable ftrace tracepoints dynamically" | 417 | bool "enable/disable function tracing dynamically" |
418 | depends on FUNCTION_TRACER | 418 | depends on FUNCTION_TRACER |
419 | depends on HAVE_DYNAMIC_FTRACE | 419 | depends on HAVE_DYNAMIC_FTRACE |
420 | default y | 420 | default y |
421 | help | 421 | help |
422 | This option will modify all the calls to ftrace dynamically | 422 | This option will modify all the calls to function tracing |
423 | (will patch them out of the binary image and replace them | 423 | dynamically (will patch them out of the binary image and |
424 | with a No-Op instruction) as they are called. A table is | 424 | replace them with a No-Op instruction) on boot up. During |
425 | created to dynamically enable them again. | 425 | compile time, a table is made of all the locations that ftrace |
426 | can function trace, and this table is linked into the kernel | ||
427 | image. When this is enabled, functions can be individually | ||
428 | enabled, and the functions not enabled will not affect | ||
429 | performance of the system. | ||
430 | |||
431 | See the files in /sys/kernel/debug/tracing: | ||
432 | available_filter_functions | ||
433 | set_ftrace_filter | ||
434 | set_ftrace_notrace | ||
426 | 435 | ||
427 | This way a CONFIG_FUNCTION_TRACER kernel is slightly larger, but | 436 | This way a CONFIG_FUNCTION_TRACER kernel is slightly larger, but |
428 | otherwise has native performance as long as no tracing is active. | 437 | otherwise has native performance as long as no tracing is active. |
429 | 438 | ||
430 | The changes to the code are done by a kernel thread that | ||
431 | wakes up once a second and checks to see if any ftrace calls | ||
432 | were made. If so, it runs stop_machine (stops all CPUS) | ||
433 | and modifies the code to jump over the call to ftrace. | ||
434 | |||
435 | config DYNAMIC_FTRACE_WITH_REGS | 439 | config DYNAMIC_FTRACE_WITH_REGS |
436 | def_bool y | 440 | def_bool y |
437 | depends on DYNAMIC_FTRACE | 441 | depends on DYNAMIC_FTRACE |