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authorLinus Torvalds <torvalds@linux-foundation.org>2013-03-11 07:54:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-03-11 07:54:29 -0700
commit7c6baa304b841673d3a55ea4fcf9a5cbf7a1674b (patch)
treea6f9970cebfb573a74a4abd06ff9caee41460e9a /kernel/trace/Kconfig
parent0cb77508252e2d0e00c5ec7e57b4be9b3f7eb24d (diff)
parentcb16b91a449afd01b85ec4e59f30449d11c4acd7 (diff)
downloadop-kernel-dev-7c6baa304b841673d3a55ea4fcf9a5cbf7a1674b.zip
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Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull perf fixes from Ingo Molnar: "Misc minor fixes mostly related to tracing" * 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: s390: Fix a header dependencies related build error tracing: update documentation of snapshot utility tracing: Do not return EINVAL in snapshot when not allocated tracing: Add help of snapshot feature when snapshot is empty ftrace: Update the kconfig for DYNAMIC_FTRACE
Diffstat (limited to 'kernel/trace/Kconfig')
-rw-r--r--kernel/trace/Kconfig24
1 files changed, 14 insertions, 10 deletions
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 192473b..fc382d6 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -414,24 +414,28 @@ 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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