Messages in this thread |  | | | Date | Wed, 10 Jun 2009 14:56:30 -0400 (EDT) | | From | Steven Rostedt <> | | Subject | Re: [PATCH 2/2] ftrace: document basic ftracer/ftracer graph needs |
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On Wed, 10 Jun 2009, Mike Frysinger wrote: > The File System > --------------- > > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig > index 417d198..be936c9 100644 > --- a/kernel/trace/Kconfig > +++ b/kernel/trace/Kconfig > @@ -14,9 +14,46 @@ config HAVE_FTRACE_NMI_ENTER > > config HAVE_FUNCTION_TRACER > bool > + help > + Implement support for the _mcount() function (or whatever your > + toolchain names it), and the ftrace_stub function (which only > + does a return). > + > + The _mcount() function should check the function pointer > + ftrace_trace_function to see if it is set to ftrace_stub. If > + it is, there is nothing for you to do -- return. If it isn't, > + then call it the same way the _mcount() function normally calls > + __mcount_internal() -- the first argument is the "frompc" while > + the second argument is the "selfpc" (adjusted to remove the size > + of the embedded _mcount() call). > + > + For example, if the function foo() calls bar(), when the bar() > + function calls _mcount(), the arguments to the tracer are: > + "frompc" - the address bar() will use to return to foo() > + "selfpc" - the address bar() (with _mcount() size adjustment)
This is too much for Kconfig.
> > config HAVE_FUNCTION_GRAPH_TRACER > bool > + help > + Update your _mcount() function to check the function pointers > + ftrace_graph_return (compare to ftrace_stub) and ftrace_graph_entry > + (compare to ftrace_graph_entry_stub). If either of those are not > + set to the relevant stub function, call the arch-specific function > + ftrace_graph_caller which in turn calls the arch-specific function > + prepare_ftrace_return. > + > + The arguments to prepare_ftrace_return() are slightly different. > + The first argument will instead be a pointer to the "frompc" -- > + typically located in the stack. This allows the function to > + hijack the return address temporarily to have it point to the > + arch-specific function return_to_handler(). For exact details of > + how to implement prepare_ftrace_return(), consult an existing port. > + It is fairly straight forward C code. > + > + The return_to_handler() function is simple as well. Have it call > + the common ftrace_return_to_handler() function. The return value > + is the original return address, so restore this to the right place > + and return.
This is also too much for Kconfig.
> > config HAVE_FUNCTION_TRACE_MCOUNT_TEST > bool > @@ -25,11 +62,17 @@ config HAVE_FUNCTION_TRACE_MCOUNT_TEST > variable at the mcount call site. Otherwise, this variable > is tested by the called function. > > + It is of course optional for arches, but does improve performance > + a bit as it prevents constant state saving and call overhead when > + the function tracer is actually disabled. > +
The above would be fine, although I would reword it a little:
This is optional for archs, but will improve performance, as it prevents constant state saving and call overhead when the function tracer tracer is active, but has been disabled.
I put in 'is active' because with dynamic function tracing it has no more overhead when disabled. We can enable function tracing, but soft disable it with a check of a bit.
> config HAVE_DYNAMIC_FTRACE > bool > > config HAVE_FTRACE_MCOUNT_RECORD > bool > + help > + See scripts/recordmcount.pl for more info.
This is fine.
-- Steve
> > config HAVE_HW_BRANCH_TRACER > bool > -- > 1.6.3.1 > >
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