Re: [PATCH] ftrace: Avoid needless updates of the ftrace function call

Steven Rostedt [off-list ref] 于2022年11月23日周三 03:17写道：

On Wed, 23 Nov 2022 10:29:28 +0800
Song Shuai [off-list ref] wrote:

quoted

quoted

@@ -2783,7 +2796,7 @@ void ftrace_modify_all_code(int command)
         * traced.
         */
        if (update) {
-               err = ftrace_update_ftrace_func(ftrace_ops_list_func);
+               err = update_ftrace_func(ftrace_ops_list_func);
                if (FTRACE_WARN_ON(err))
                        return;
        }

@@ -2799,7 +2812,7 @@ void ftrace_modify_all_code(int command)
                /* If irqs are disabled, we are in stop machine */
                if (!irqs_disabled())
                        smp_call_function(ftrace_sync_ipi, NULL, 1);
-               err = ftrace_update_ftrace_func(ftrace_trace_function);
+               err = update_ftrace_func(ftrace_trace_function);

The helper function should only serve the ftrace_ops_list_func.

And ftrace_trace_function is always different in this function with
FTRACE_UPDATE_TRACE_FUNC command.

So this place should be left as it is.

But it is needed to update the static variable. Without this change,
then save_func will get set to ftrace_ops_list_func and never change
after that and then the update to ftrace_ops_list_func will stop happening.

-- Steve

Yes, you're right. Thx for your explanation.
-- Song