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

Frederic Weisbecker
2009-04-08T17:40:59Z

On Wed, Apr 08, 2009 at 06:09:15PM +0200, Ingo Molnar wrote:
>
> (replying to old mail - working down my awful email backlog)
>
> do we still need this for -tip?
>
> Ingo

Yes. It drops a small overhead on the function graph tracer.

Thanks,
Frederic.

> * Steven Rostedt <rostedt@goodmis.org> 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