diff options
Diffstat (limited to 'kernel')
-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 36567564e221..b516a8e19d51 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig | |||
@@ -429,24 +429,28 @@ config PROBE_EVENTS | |||
429 | def_bool n | 429 | def_bool n |
430 | 430 | ||
431 | config DYNAMIC_FTRACE | 431 | config DYNAMIC_FTRACE |
432 | bool "enable/disable ftrace tracepoints dynamically" | 432 | bool "enable/disable function tracing dynamically" |
433 | depends on FUNCTION_TRACER | 433 | depends on FUNCTION_TRACER |
434 | depends on HAVE_DYNAMIC_FTRACE | 434 | depends on HAVE_DYNAMIC_FTRACE |
435 | default y | 435 | default y |
436 | help | 436 | help |
437 | This option will modify all the calls to ftrace dynamically | 437 | This option will modify all the calls to function tracing |
438 | (will patch them out of the binary image and replace them | 438 | dynamically (will patch them out of the binary image and |
439 | with a No-Op instruction) as they are called. A table is | 439 | replace them with a No-Op instruction) on boot up. During |
440 | created to dynamically enable them again. | 440 | compile time, a table is made of all the locations that ftrace |
441 | can function trace, and this table is linked into the kernel | ||
442 | image. When this is enabled, functions can be individually | ||
443 | enabled, and the functions not enabled will not affect | ||
444 | performance of the system. | ||
445 | |||
446 | See the files in /sys/kernel/debug/tracing: | ||
447 | available_filter_functions | ||
448 | set_ftrace_filter | ||
449 | set_ftrace_notrace | ||
441 | 450 | ||
442 | This way a CONFIG_FUNCTION_TRACER kernel is slightly larger, but | 451 | This way a CONFIG_FUNCTION_TRACER kernel is slightly larger, but |
443 | otherwise has native performance as long as no tracing is active. | 452 | otherwise has native performance as long as no tracing is active. |
444 | 453 | ||
445 | The changes to the code are done by a kernel thread that | ||
446 | wakes up once a second and checks to see if any ftrace calls | ||
447 | were made. If so, it runs stop_machine (stops all CPUS) | ||
448 | and modifies the code to jump over the call to ftrace. | ||
449 | |||
450 | config DYNAMIC_FTRACE_WITH_REGS | 454 | config DYNAMIC_FTRACE_WITH_REGS |
451 | def_bool y | 455 | def_bool y |
452 | depends on DYNAMIC_FTRACE | 456 | depends on DYNAMIC_FTRACE |