linux-kernel - Re: [v2 PATCH] ftrace: Speed up recordmcount

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Date:	Wed, 27 Oct 2010 22:21:18 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Wu Zhangjin <wuzhangjin@...il.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	John Reiser <jreiser@...wagon.com>,
	Sam Ravnborg <sam@...nborg.org>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	Michal Marek <mmarek@...e.cz>
Subject: Re: [v2 PATCH] ftrace: Speed up recordmcount

Michal,

Can you give an Acked-by: on this patch?

Thanks!

-- Steve


On Thu, 2010-10-28 at 00:24 +0800, Wu Zhangjin wrote:
> From: Wu Zhangjin <wuzhangjin@...il.com>
> 
> cmd_record_mcount is used to locate the _mcount symbols in the object
> files, only the files compiled with -pg has the _mcount symbol, so, it
> is only needed for such files, but the current cmd_record_mcount is used
> for all of the object files, so, we need to fix it and speed it up.
> 
> Since -pg may be removed by the method used in kernel/trace/Makefile:
> 
> ORIG_CFLAGS := $(KBUILD_CFLAGS)
> KBUILD_CFLAGS = $(subst -pg,,$(ORIG_CFLAGS))
> 
> Or may be removed by the method used in arch/x86/kernel/Makefile:
> 
> CONFIG_REMOVE_file.o = -pg
> 
> So, we must check the last variable stores the compiling flags, that is
> c_flags(Please refer to cmd_cc_o_c and rule_cc_o_c defined in
> scripts/Makefile.build) and since the CFLAGS_REMOVE_file.o is already
> filtered in _c_flags(Please refer to scripts/Makefile.lib) and _c_flags
> has less symbols, therefore, we only need to check _c_flags.
> 
> ---------------
> Changes from v1:
> 
>   o Don't touch Makefile for CONFIG_FTRACE_MCOUNT_RECORD is enough
>   o Use _c_flags intead of KBUILD_CFLAGS to cover CONFIG_REMOVE_file.o = -pg
>   (feedback from Steven Rostedt <rostedt@...dmis.org>)
> 
> Signed-off-by: Wu Zhangjin <wuzhangjin@...il.com>
> ---
>  scripts/Makefile.build |   13 +++++++++----
>  1 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 5ad25e1..0ad6108 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -214,17 +214,22 @@ ifdef BUILD_C_RECORDMCOUNT
>  # The empty.o file is created in the make process in order to determine
>  #  the target endianness and word size. It is made before all other C
>  #  files, including recordmcount.
> -cmd_record_mcount = if [ $(@) != "scripts/mod/empty.o" ]; then			\
> -			$(objtree)/scripts/recordmcount "$(@)";			\
> -		    fi;
> +sub_cmd_record_mcount =					\
> +	if [ $(@) != "scripts/mod/empty.o" ]; then	\
> +		$(objtree)/scripts/recordmcount "$(@)";	\
> +	fi;
>  else
> -cmd_record_mcount = set -e ; perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
> +sub_cmd_record_mcount = set -e ; perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
>  	"$(if $(CONFIG_CPU_BIG_ENDIAN),big,little)" \
>  	"$(if $(CONFIG_64BIT),64,32)" \
>  	"$(OBJDUMP)" "$(OBJCOPY)" "$(CC) $(KBUILD_CFLAGS)" \
>  	"$(LD)" "$(NM)" "$(RM)" "$(MV)" \
>  	"$(if $(part-of-module),1,0)" "$(@)";
>  endif
> +cmd_record_mcount = 						\
> +	if [ "$(findstring -pg,$(_c_flags))" == "-pg" ]; then	\
> +		$(sub_cmd_record_mcount)			\
> +	fi;
>  endif
>  
>  define rule_cc_o_c


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