-When dynamic ftrace is initialized, it calls kstop_machine to make
-the machine act like a uniprocessor so that it can freely modify code
-without worrying about other processors executing that same code. At
-initialization, the mcount calls are changed to call a "record_ip"
-function. After this, the first time a kernel function is called,
-it has the calling address saved in a hash table.
-
-Later on the ftraced kernel thread is awoken and will again call
-kstop_machine if new functions have been recorded. The ftraced thread
-will change all calls to mcount to "nop". Just calling mcount
-and having mcount return has shown a 10% overhead. By converting
-it to a nop, there is no measurable overhead to the system.
+At compile time every C file object is run through the
+recordmcount.pl script (located in the scripts directory). This
+script will process the C object using objdump to find all the
+locations in the .text section that call mcount. (Note, only
+the .text section is processed, since processing other sections
+like .init.text may cause races due to those sections being freed).
+
+A new section called "__mcount_loc" is created that holds references
+to all the mcount call sites in the .text section. This section is
+compiled back into the original object. The final linker will add
+all these references into a single table.
+
+On boot up, before SMP is initialized, the dynamic ftrace code
+scans this table and updates all the locations into nops. It also
+records the locations, which are added to the available_filter_functions
+list. Modules are processed as they are loaded and before they are
+executed. When a module is unloaded, it also removes its functions from
+the ftrace function list. This is automatic in the module unload
+code, and the module author does not need to worry about it.
+
+When tracing is enabled, kstop_machine is called to prevent races
+with the CPUS executing code being modified (which can cause the
+CPU to do undesireable things), and the nops are patched back
+to calls. But this time, they do not call mcount (which is just
+a function stub). They now call into the ftrace infrastructure.