tracing: add function profiler
Impact: new profiling feature
This patch adds a function profiler. In debugfs/tracing/ two new
files are created.
function_profile_enabled - to enable or disable profiling
trace_stat/functions - the profiled functions.
For example:
echo 1 > /debugfs/tracing/function_profile_enabled
./hackbench 50
echo 0 > /debugfs/tracing/function_profile_enabled
yields:
cat /debugfs/tracing/trace_stat/functions
Function Hit
-------- ---
_spin_lock 10106442
_spin_unlock 10097492
kfree 6013704
_spin_unlock_irqrestore 4423941
_spin_lock_irqsave 4406825
__phys_addr 4181686
__slab_free 4038222
dput 4030130
path_put 4023387
unroll_tree_refs 4019532
[...]
The most hit functions are listed first. Functions that are not
hit are not listed.
This feature depends on and uses dynamic function tracing. When the
function profiling is disabled, no overhead occurs. But it still
takes up around 300KB to hold the data, thus it is not recomended
to keep it enabled for systems low on memory.
When a '1' is echoed into the function_profile_enabled file, the
counters for is function is reset back to zero. Thus you can see what
functions are hit most by different programs.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 8a4d729..95e9ad5 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -105,6 +105,7 @@
This is done by setting the current return address on the current
task structure into a stack of calls.
+
config IRQSOFF_TRACER
bool "Interrupts-off Latency Tracer"
default n
@@ -376,6 +377,24 @@
were made. If so, it runs stop_machine (stops all CPUS)
and modifies the code to jump over the call to ftrace.
+config FUNCTION_PROFILER
+ bool "Kernel function profiler"
+ depends on DYNAMIC_FTRACE
+ default n
+ help
+ This option enables the kernel function profiler. When the dynamic
+ function tracing is enabled, a counter is added into the function
+ records used by the dynamic function tracer. A file is created in
+ debugfs called function_profile_enabled which defaults to zero.
+ When a 1 is echoed into this file profiling begins, and when a
+ zero is entered, profiling stops. A file in the trace_stats
+ directory called functions, that show the list of functions that
+ have been hit and their counters.
+
+ This takes up around 320K more memory.
+
+ If in doubt, say N
+
config FTRACE_MCOUNT_RECORD
def_bool y
depends on DYNAMIC_FTRACE
