Re: mod_devicetable: Make dmi_strmatch.substr const char *

From: Rusty Russell <rusty@rustcorp.com.au>
To: Joe Perches <joe@perches.com>,
	One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: David Woodhouse <dwmw2@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Quentin Casasnovas <quentin.casasnovas@oracle.com>,
	Michal Marek <mmarek@suse.cz>,
	Andreas Schwab <schwab@linux-m68k.org>
Subject: Re: mod_devicetable: Make dmi_strmatch.substr const char *
Date: Wed, 20 May 2015 14:49:03 +0930	[thread overview]
Message-ID: <878ucjhlmg.fsf@rustcorp.com.au> (raw)
In-Reply-To: <1432063162.2870.199.camel@perches.com>

Joe Perches <joe@perches.com> writes:
> On Tue, 2015-05-19 at 16:56 +0100, One Thousand Gnomes wrote:
>> On Tue, 19 May 2015 07:46:58 +0100 David Woodhouse <dwmw2@infradead.org> wrote:
>> > On Mon, 2015-05-18 at 17:07 -0700, Joe Perches wrote:
>> > > changed dmi_strmatch.substr from char * to char[79];
>> > > 
>> > > Changing it back to const char * would shrink an x86-64
>> > > defconfig more than 100KB.
>> > > 
>> > > $ size vmlinux.old vmlinux.new
>> > >     text    data     bss      dec    hex filename
>> > > 11941725 1825624 1085440 14852789 e2a2b5 vmlinux.old
>> > > 11921172 1730648 1085440 14737260 e0df6c vmlinux.new
>> 
>> What percentage of those are __initdata ?
>
> old: 17 .init.data    000876b0  ffffffff81f9e000  0000000001f9e000  0139e000  2**12
> new: 17 .init.data    000711b0  ffffffff81f9d000  0000000001f9d000  0139d000  2**12
>
> .init.data: 0x876b0 - 0x711b0 = 0x16500 (91392)
>    vmlinux: 14852789 - 14737260 = 115529
>
> so there's ~25KB delta that's not .init.data.
>
> The longest DMI_MATCH substr I found was 40 chars, so
> there's some value in reducing the substr size of 79
> to something shorter like 47 to reduce 80*4=320 to
> 48*4=192 per use.

This patch is nice and trivial.

But it seems the file2alias code was rewritten in 2013 by Andreas Schwab
<schwab@linux-m68k.org>, and SOB Michal Marek <mmarek@suse.cz>, without
going through me.  Annoying, since they had to hack it because people
screwed up mod_devicetable.h with arch-dependent layouts :(

I guess that means Michal is the maintainer now, so I've CC'd him.

Cheers,
Rusty.

> $ grep-2.5.4 -rP  --include=*.[ch] "\bDMI_(?:EXACT_)?MATCH\s*\(\s*\w+\s*,\s*\"[^\"]*" *| \
>   grep -oh '"[^"]*"' | \
>   sed 's/"//g' | sort | uniq | \
>   awk '{print length($0), "	", $0}'| \
>   sort -rn | head -10
> 39     Matsushita Electric Industrial Co.,Ltd.
> 35     ASUS PR-DLS ACPI BIOS Revision 1010
> 34     Micro-Star International Co., Ltd.
> 34     Award Software International, Inc.
> 34     900X3C/900X3D/900X3E/900X4C/900X4D
> 34     370R4E/370R4V/370R5E/3570RE/370R5V
> 33     MICRO-STAR INTERNATIONAL CO., LTD
> 32     MV85010A.86A.0016.P07.0201251536
> 32     MO81010A.86A.0008.P04.0004170800
> 32     ASUS A7V ACPI BIOS Revision 1007
>
> Changing substr from 79 to 47 reduces .init.data a bit
> (different -next version)
>
> old: 17 .init.data    00081718  ffffffff81f84000  0000000001f84000  01384000  2**12
> new: 17 .init.data    00076598  ffffffff81f84000  0000000001f84000  01384000  2**12
>
> .init.data: 0x81718 - 0x76598 = 0xb180 (45440)
>
> Unless/until modpost is updated, maybe this patch is OK:
> ---
>  include/linux/mod_devicetable.h | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
> index 3bfd567..279f1be 100644
> --- a/include/linux/mod_devicetable.h
> +++ b/include/linux/mod_devicetable.h
> @@ -462,7 +462,11 @@ enum dmi_field {
>  struct dmi_strmatch {
>  	unsigned char slot:7;
>  	unsigned char exact_match:1;
> -	char substr[79];
> +#ifdef CONFIG_MODULES
> +	char substr[47];
> +#else
> +	const char *substr;
> +#endif
>  };
>  
>  struct dmi_system_id {