linux-kernel - Re: [PATCH] tracing/function-graph-tracer: don't profile branches on graph tracer

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Date:	Mon, 23 Mar 2009 14:46:27 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/function-graph-tracer: don't profile branches
 on graph tracer


On Sun, 22 Mar 2009, Frederic Weisbecker wrote:

> Impact: fix slow tracing
> 
> The core kernel tracing is protected against soft branch profiling, but
> not the x86 ftrace arch part. Let's fix it.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
>  arch/x86/kernel/Makefile |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 599e9a7..8d9b3f9 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -13,6 +13,7 @@ CFLAGS_REMOVE_rtc.o = -pg
>  CFLAGS_REMOVE_paravirt-spinlocks.o = -pg
>  CFLAGS_REMOVE_ftrace.o = -pg
>  CFLAGS_REMOVE_early_printk.o = -pg
> +CFLAGS_ftrace.o += -DDISABLE_BRANCH_PROFILING
>  endif
>  

Actually, I prefer not to do this. I do use the branch profiling on 
ftrace, to see where the hot paths are.

-- Steve

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