On Tue, 1 Dec 2015 14:42:36 +0100
Jiri Olsa <jo...@redhat.com> wrote:
> On Mon, Nov 30, 2015 at 05:36:40PM -0500, Steven Rostedt wrote:
> >
> > [ Jiri, can you take a look at this. You can also apply it on top of my
> > branch ftrace/core, and run any specific tests. I just need to nuke
> > that control structure for further updates with ftrace. ]
> >
> >
> > Currently perf has its own list function within the ftrace infrastructure
> > that seems to be used only to allow for it to have per-cpu disabling as well
> > as a check to make sure that it's not called while RCU is not watching. It
> > uses something called the "control_ops" which is used to iterate over ops
> > under it with the control_list_func().
> >
> > The problem is that this control_ops and control_list_func unnecessarily
> > complicates the code. By replacing FTRACE_OPS_FL_CONTROL with two new flags
> > (FTRACE_OPS_FL_RCU and FTRACE_OPS_FL_PER_CPU) we can remove all the code
> > that is special with the control ops and add the needed checks within the
> > generic ftrace_list_func().
>
> hum,
> do we need also change for the trampoline, something like below?
>
> I needed attached patch to get the perf ftrace:function
> event work properly..
Hmm, I thought that I forced the list function when RCU or PER_CPU
was set. Oh wait. I have CONFIG_PREEMPT set, which will change the
logic slightly. I'm guessing you have PREEMPT_VOLUNTARY set. I'll try
that out.
>
> thanks,
> jirka
>
>
> ---
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index c4d881200d1f..2705ac2f3487 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5179,6 +5179,26 @@ static void ftrace_ops_recurs_func(unsigned long ip,
> unsigned long parent_ip,
> trace_clear_recursion(bit);
> }
>
> +static void ftrace_ops_per_cpu_func(unsigned long ip, unsigned long
> parent_ip,
> + struct ftrace_ops *op, struct pt_regs *regs)
> +{
> + int bit;
> +
> + bit = trace_test_and_set_recursion(TRACE_LIST_START, TRACE_LIST_MAX);
> + if (bit < 0)
> + return;
> +
> + preempt_disable_notrace();
> +
> + if ((!(op->flags & FTRACE_OPS_FL_RCU) || rcu_is_watching()) &&
> + (!(op->flags & FTRACE_OPS_FL_PER_CPU) ||
> !ftrace_function_local_disabled(op))) {
> + op->func(ip, parent_ip, op, regs);
> + }
> +
> + preempt_enable_notrace();
> + trace_clear_recursion(bit);
> +}
> +
> /**
> * ftrace_ops_get_func - get the function a trampoline should call
> * @ops: the ops to get the function for
> @@ -5192,6 +5212,11 @@ static void ftrace_ops_recurs_func(unsigned long ip,
> unsigned long parent_ip,
> */
> ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops)
> {
> + if (ops->flags & (FTRACE_OPS_FL_PER_CPU|FTRACE_OPS_FL_RCU)) {
> + printk("used per cpu trampoline function\n");
> + return ftrace_ops_per_cpu_func;
I have a slight different idea on how to handle this.
-- Steve
> + }
> +
> /*
> * If the func handles its own recursion, call it directly.
> * Otherwise call the recursion protected function that
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