Messages in this thread | | | Date | Wed, 8 Apr 2009 19:40:43 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH][GIT PULL] x86, function-graph: only save return values on x86_64 |
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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
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