Re: Ftrace for Microblaze - notrace

[Michal Simek]

Steven Rostedt wrote:
> On Tue, 2009-11-03 at 14:32 +0100, Michal Simek wrote:
> > Hi Thomas, Ingo, Steven and others
> >
> > I am working on ftrace support for Microblaze. I have done basic ftrace
> > support - initcall, kmemtrace and other.
> > Currently I am working on function trace support.  I did asm code as is
> > written in Documentation/trace/ftrace-design.txt.
> >
> > I have two poins/questions.
> >
> > I desided to use HAVE_FUNCTION_TRACE_MCOUNT_TEST - just test 
> > function_trace_stop in asm code - that shouldn't be a problem.
>
> Yeah, and if you don't have that, it is taken care of in the generic
> code too.

jj, I know - asm checking is just two instruction - that's why I use it.

> > I disable -pg in main Makefile because not work for me (more info below) 
> > and I enable it just for two file in arch/microblaze (irq.c and intc.c) 
> > - recompile kernel and test. Log is below and you can see that I am able 
> > to see output for function. That's why I think that my mcount function 
> > should be correct. Am I right?
> >
> > uclinux login: root
> > Password:
> > # cd ; mkdir /debug; mount -t debugfs none /debug; cat 
> > /debug/tracing/available_
> > tracers; echo function > /debug/tracing/current_tracer;echo 1 > 
> > /debug/tracing/t
> > racing_enabled;cat /debug/tracing/trace | head -n 10
> > wakeup_rt wakeup function sched_switch nop
> > # tracer: function
> > #
> > #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
> > #              | |       |          |         |
> >                sh-52    [000]   184.940000: irq_call <-do_IRQ
> >                sh-52    [000]   184.940000: do_IRQ <-get_irq
> >                sh-52    [000]   184.940000: handle_level_irq <-intc_mask_ack
> >                sh-52    [000]   184.950000: handle_level_irq 
> > <-intc_enable_or_unmask
> >                sh-52    [000]   184.950000: do_IRQ <-get_irq
> >                sh-52    [000]   184.950000: handle_level_irq <-intc_mask_ack
> > #
> >
> >
> > When is used -pg flag kernel stops when I enable function tracer.
> > Interesting is that freeze than I setup function tracing (echo function 
> >  > .../current/tracer). Is it correct behavior? I think that trace 
> > should start after (echo 1>  .../tracing_enabled).
>
> No, tracing_enabled is default on and should not be used (may go away).
> Tracing starts as soon as you echo function into current_tracer.

ok


> > The next thing is about annotation notrace. I look at all arch. Is there 
> > any algorithm which function should use it? I think that this could be a 
> >   reason why I my kernel freeze when enable function tracer.
> >
> > I tested to add -pg flag for process.c file and after it kernel freeze 
> > too. Is it mean that problem could be there?
>
> Probably.

Is there any manual or instruction which functions are dangerous and 
especially why?


> > Any other suggestion?
>
> Just remember that -pg is very intrusive. I don't know your arch, nor
> have I seen the code you did to update it. You can disable the -pg from
> process.c by adding in the Makefile:
>
> CFLAGS_REMOVE_process.o = -pg

jj, I know how to do it.

> And that will keep the process.c from being compiled with it. There may
> be other files in the arch that should not have it. There's several in
> x86 and in PowerPC.

Do you know why they exclude it?

Can I use any special debug features? I mean I look at kernel.h and 
there are some trace_printk function - but they don't work for me. Is it 
possible to use them or not?

Thanks,
Michal

> -- Steve

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