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authorIngo Molnar <mingo@kernel.org>2013-02-28 10:12:04 +0100
committerIngo Molnar <mingo@kernel.org>2013-02-28 10:12:04 +0100
commita335358f52aec4397594043ac799d15f92e728dd (patch)
tree8146f2c71be7a05ef1615a431adecd9ec46d3e2f /kernel
parentff1fb5f6b4925a536ffb8171e5f2dbd01ccfeb97 (diff)
parentdb05021d49a994ee40a9735d9c3cb0060c9babb8 (diff)
downloadop-kernel-dev-a335358f52aec4397594043ac799d15f92e728dd.zip
op-kernel-dev-a335358f52aec4397594043ac799d15f92e728dd.tar.gz
Merge branch 'tip/perf/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace into perf/urgent
Pull an ftrace Kconfig help text fix from Steve Rostedt. Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/Kconfig24
1 files changed, 14 insertions, 10 deletions
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 3656756..b516a8e 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -429,24 +429,28 @@ config PROBE_EVENTS
def_bool n
config DYNAMIC_FTRACE
- bool "enable/disable ftrace tracepoints dynamically"
+ bool "enable/disable function tracing dynamically"
depends on FUNCTION_TRACER
depends on HAVE_DYNAMIC_FTRACE
default y
help
- This option will modify all the calls to ftrace dynamically
- (will patch them out of the binary image and replace them
- with a No-Op instruction) as they are called. A table is
- created to dynamically enable them again.
+ This option will modify all the calls to function tracing
+ dynamically (will patch them out of the binary image and
+ replace them with a No-Op instruction) on boot up. During
+ compile time, a table is made of all the locations that ftrace
+ can function trace, and this table is linked into the kernel
+ image. When this is enabled, functions can be individually
+ enabled, and the functions not enabled will not affect
+ performance of the system.
+
+ See the files in /sys/kernel/debug/tracing:
+ available_filter_functions
+ set_ftrace_filter
+ set_ftrace_notrace
This way a CONFIG_FUNCTION_TRACER kernel is slightly larger, but
otherwise has native performance as long as no tracing is active.
- The changes to the code are done by a kernel thread that
- wakes up once a second and checks to see if any ftrace calls
- were made. If so, it runs stop_machine (stops all CPUS)
- and modifies the code to jump over the call to ftrace.
-
config DYNAMIC_FTRACE_WITH_REGS
def_bool y
depends on DYNAMIC_FTRACE
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