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Date: Wed, 3 Dec 2008 09:13:01 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH 4/5] ftrace: function graph return for function entry
Message-ID: <20081203081301.GF21006@elte.hu>
References: <20081203045001.367443457@goodmis.org> <20081203045044.002248353@goodmis.org>
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* Steven Rostedt <rostedt@goodmis.org> wrote:

> From: Steven Rostedt <srostedt@redhat.com>
> 
> Impact: feature, let entry function decide to trace or not
> 
> This patch lets the graph tracer entry function decide if the tracing 
> should be done at the end as well. This requires all function graph 
> entry functions return 1 if it should trace, or 0 if the return should 
> not be traced.

> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 47aa5f0..cef05a2 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -119,6 +119,9 @@ ENTRY(mcount)
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>  	cmpq $ftrace_stub, ftrace_graph_return
>  	jnz ftrace_graph_caller
> +
> +	cmpq $ftrace_graph_entry_stub, ftrace_graph_entry
> +	jnz ftrace_graph_caller

hm, that's in the hotpath. What's the point of this? Do we want some sort 
of configuration vector that allows per function graphing versus 
entry-only traces?

	Ingo