linux-kernel - Re: [PATCH] fgraph: Remove redundant ftrace_graph_notrace

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Date:   Tue, 30 Jul 2019 12:15:27 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fgraph: Remove redundant ftrace_graph_notrace_addr()
 test

On Tue, 30 Jul 2019 22:08:50 +0800
Changbin Du <changbin.du@...il.com> wrote:

> We already have tested it before. The second one should be removed.
> With this change, the performance should have little improvement.
> 
> Fixes: 9cd2992f2d6c ("fgraph: Have set_graph_notrace only affect function_graph tracer")

Thanks! I think this should even be marked for stable. Not really a bad
bug, but a bug none the less.

-- Steve


> Signed-off-by: Changbin Du <changbin.du@...il.com>
> ---
>  kernel/trace/trace_functions_graph.c | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 69ebf3c2f1b5..78af97163147 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -137,6 +137,13 @@ int trace_graph_entry(struct ftrace_graph_ent *trace)
>  	if (trace_recursion_test(TRACE_GRAPH_NOTRACE_BIT))
>  		return 0;
>  
> +	/*
> +	 * Do not trace a function if it's filtered by set_graph_notrace.
> +	 * Make the index of ret stack negative to indicate that it should
> +	 * ignore further functions.  But it needs its own ret stack entry
> +	 * to recover the original index in order to continue tracing after
> +	 * returning from the function.
> +	 */
>  	if (ftrace_graph_notrace_addr(trace->func)) {
>  		trace_recursion_set(TRACE_GRAPH_NOTRACE_BIT);
>  		/*
> @@ -155,16 +162,6 @@ int trace_graph_entry(struct ftrace_graph_ent *trace)
>  	if (ftrace_graph_ignore_irqs())
>  		return 0;
>  
> -	/*
> -	 * Do not trace a function if it's filtered by set_graph_notrace.
> -	 * Make the index of ret stack negative to indicate that it should
> -	 * ignore further functions.  But it needs its own ret stack entry
> -	 * to recover the original index in order to continue tracing after
> -	 * returning from the function.
> -	 */
> -	if (ftrace_graph_notrace_addr(trace->func))
> -		return 1;
> -
>  	/*
>  	 * Stop here if tracing_threshold is set. We only write function return
>  	 * events to the ring buffer.