Re: [PATCH][GIT PULL] x86, function-graph: only save return values on x86_64

Jaswinder Singh Rajput
2009-03-25T20:46:53Z

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@redhat.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@redhat.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