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

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Message-ID: <AANLkTimS7YsZo+AGyTJq+G4kqsviRMRbdgt3NqZgEUws@mail.gmail.com>
Date:	Tue, 9 Nov 2010 13:35:40 +0800
From:	wu zhangjin <wuzhangjin@...il.com>
To:	rostedt@...dmis.org
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

Hi, Steve

On 10/29/10, Michal Marek <mmarek@...e.cz> wrote:
> On 27.10.2010 18:24, 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
>
> CFLAGS_REMOVE_file.o
>

Did you apply this patch, should I fix this typo and resend it to you?

Best Regards,
Wu Zhangjin

>
>> 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>
>
> Acked-by: Michal Marek <mmarek@...e.cz>
>
>
>> ---
>>  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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