[PATCH v14 19/19] fgraph: Skip recording calltime/rettime if it is not nneeded

@@ -1160,6 +1160,8 @@ struct fgraph_ops {
 	void				*private;
 	trace_func_graph_ent_t		saved_func;
 	int				idx;
+	/* If skip_timestamp is true, this does not record timestamps. */
+	bool				skip_timestamp;
 };
 
 void *fgraph_reserve_data(int idx, int size_bytes);

@@ -174,6 +174,7 @@ int ftrace_graph_active;
 
 static struct fgraph_ops *fgraph_array[FGRAPH_ARRAY_SIZE];
 static unsigned long fgraph_array_bitmask;
+static bool fgraph_skip_timestamp;
 
 /* LRU index table for fgraph_array */
 static int fgraph_lru_table[FGRAPH_ARRAY_SIZE];

@@ -557,7 +558,11 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func,
 		return -EBUSY;
 	}
 
-	calltime = trace_clock_local();
+	/* This is not really 'likely' but for keeping the least path to be faster. */
+	if (likely(fgraph_skip_timestamp))
+		calltime = 0LL;
+	else
+		calltime = trace_clock_local();
 
 	offset = READ_ONCE(current->curr_ret_stack);
 	ret_stack = RET_STACK(current, offset);

@@ -728,6 +733,12 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
 	*ret = ret_stack->ret;
 	trace->func = ret_stack->func;
 	trace->calltime = ret_stack->calltime;
+	/* This is not really 'likely' but for keeping the least path to be faster. */
+	if (likely(!trace->calltime))
+		trace->rettime = 0LL;
+	else
+		trace->rettime = trace_clock_local();
+
 	trace->overrun = atomic_read(&current->trace_overrun);
 	trace->depth = current->curr_ret_depth;
 	/*

@@ -788,7 +799,6 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, unsigned long frame_pointe
 		return (unsigned long)panic;
 	}
 
-	trace.rettime = trace_clock_local();
 	if (fregs)
 		ftrace_regs_set_instruction_pointer(fregs, ret);
 

@@ -1248,6 +1258,24 @@ static void ftrace_graph_disable_direct(bool disable_branch)
 	fgraph_direct_gops = &fgraph_stub;
 }
 
+static void update_fgraph_skip_timestamp(void)
+{
+	int i;
+
+	for (i = 0; i < FGRAPH_ARRAY_SIZE; i++) {
+		struct fgraph_ops *gops = fgraph_array[i];
+
+		if (gops == &fgraph_stub)
+			continue;
+
+		if (!gops->skip_timestamp) {
+			fgraph_skip_timestamp = false;
+			return;
+		}
+	}
+	fgraph_skip_timestamp = true;
+}
+
 int register_ftrace_graph(struct fgraph_ops *gops)
 {
 	int command = 0;

@@ -1271,6 +1299,7 @@ int register_ftrace_graph(struct fgraph_ops *gops)
 	gops->idx = i;
 
 	ftrace_graph_active++;
+	update_fgraph_skip_timestamp();
 
 	if (ftrace_graph_active == 2)
 		ftrace_graph_disable_direct(true);

@@ -1303,6 +1332,7 @@ int register_ftrace_graph(struct fgraph_ops *gops)
 		ftrace_graph_active--;
 		gops->saved_func = NULL;
 		fgraph_lru_release_index(i);
+		update_fgraph_skip_timestamp();
 	}
 out:
 	mutex_unlock(&ftrace_lock);

@@ -1326,8 +1356,8 @@ void unregister_ftrace_graph(struct fgraph_ops *gops)
 		goto out;
 
 	fgraph_array[gops->idx] = &fgraph_stub;
-
 	ftrace_graph_active--;
+	update_fgraph_skip_timestamp();
 
 	if (!ftrace_graph_active)
 		command = FTRACE_STOP_FUNC_RET;

@@ -345,6 +345,7 @@ NOKPROBE_SYMBOL(fprobe_return);
 static struct fgraph_ops fprobe_graph_ops = {
 	.entryfunc	= fprobe_entry,
 	.retfunc	= fprobe_return,
+	.skip_timestamp = true,
 };
 static int fprobe_graph_active;