linux-kernel - Re: [PATCH][GIT PULL] x86, function-graph: only save return values on x86

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Message-Id: <1238013934.2500.81.camel@ht.satnam>
Date:	Thu, 26 Mar 2009 02:15:34 +0530
From:	Jaswinder Singh Rajput <jaswinder@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux kernel <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Tim Bird <tim.bird@...sony.com>,
	Ingo Molnar <mingo@...hat.com>,
	Abhishek Sagar <sagar.abhishek@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH][GIT PULL] x86, function-graph: only save return values
 on x86_64

On Wed, 2009-03-25 at 16:27 -0400, Steven Rostedt wrote:
> Ingo,
> 
> Please pull the latest tip/tracing/function-graph tree, which can be found at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
> tip/tracing/function-graph
> 
> 
> Steven Rostedt (1):
>       x86, function-graph: only save return values on x86_64
> 
> ----
>  arch/x86/kernel/entry_64.S |   19 +++----------------
>  1 files changed, 3 insertions(+), 16 deletions(-)
> ---------------------------
> commit d5b754b2208b1c22691a7cd5d1a65398b5973d74
> Author: Steven Rostedt <srostedt@...hat.com>
> Date:   Wed Mar 25 14:30:04 2009 -0400
> 
>     x86, function-graph: only save return values on x86_64
>     
>     Impact: speed up
>     
>     The return to handler portion of the function graph tracer should only
>     need to save the return values. The caller already saved off the
>     registers that the callee can modify. The returning function already
>     saved the registers it modified. When we call our own trace function
>     it too will save the registers that the callee must restore.
>     
>     There's no reason to save off anything more that the registers used
>     to return the values.
>     
>     Note, I did a complete kernel build with this modification and the
>     function graph tracer running on x86_64.
>     
>     Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> 
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index a331ec3..1ac9986 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -147,27 +147,14 @@ END(ftrace_graph_caller)
>  GLOBAL(return_to_handler)
>  	subq  $80, %rsp
>  
> +	/* Save the return values */
>  	movq %rax, (%rsp)
> -	movq %rcx, 8(%rsp)
> -	movq %rdx, 16(%rsp)
> -	movq %rsi, 24(%rsp)
> -	movq %rdi, 32(%rsp)
> -	movq %r8, 40(%rsp)
> -	movq %r9, 48(%rsp)
> -	movq %r10, 56(%rsp)
> -	movq %r11, 64(%rsp)
> +	movq %rdx, 8(%rsp)
>  
>  	call ftrace_return_to_handler
>  
>  	movq %rax, 72(%rsp)
> -	movq 64(%rsp), %r11
> -	movq 56(%rsp), %r10
> -	movq 48(%rsp), %r9
> -	movq 40(%rsp), %r8
> -	movq 32(%rsp), %rdi
> -	movq 24(%rsp), %rsi
> -	movq 16(%rsp), %rdx
> -	movq 8(%rsp), %rcx
> +	movq 8(%rsp), %rdx
>  	movq (%rsp), %rax
>  	addq $72, %rsp
>  	retq

hmm, is this gonna work:
	movq %rax, 16(%rsp)
	movq 8(%rsp), %rdx
 	movq (%rsp), %rax
 	addq $16, %rsp
 	retq

--
JSR

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