linux-kernel - Re: [PATCH] ftrace: Remove use of control list and ops

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Message-ID: <20151201134213.GA14155@krava.brq.redhat.com>
Date:	Tue, 1 Dec 2015 14:42:36 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] ftrace: Remove use of control list and ops

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..

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;
+	}
+
 	/*
 	 * If the func handles its own recursion, call it directly.
 	 * Otherwise call the recursion protected function that
--
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