From: Joe Perches <joe@perches.com>
To: Colin Ian King <colin.king@canonical.com>,
Andrzej Hajda <a.hajda@samsung.com>,
Neil Armstrong <narmstrong@baylibre.com>,
Robert Foss <robert.foss@linaro.org>,
Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
Jonas Karlman <jonas@kwiboo.se>,
Jernej Skrabec <jernej.skrabec@gmail.com>,
David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
dri-devel@lists.freedesktop.org
Cc: kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/bridge/tc358767: make the array ext_div static const, makes object smaller
Date: Thu, 19 Aug 2021 07:40:41 -0700 [thread overview]
Message-ID: <3da667b1b415b19325c034dcb389a201fa46cfd3.camel@perches.com> (raw)
In-Reply-To: <913b96bc-f5c4-1a26-c5f7-70a9d0ab3f53@canonical.com>
On Thu, 2021-08-19 at 14:54 +0100, Colin Ian King wrote:
> On 19/08/2021 14:51, Joe Perches wrote:
> > On Thu, 2021-08-19 at 14:38 +0100, Colin King wrote:
> > > From: Colin Ian King <colin.king@canonical.com>
> > >
> > > Don't populate the array ext_div on the stack but instead it
> > > static const. Makes the object code smaller by 118 bytes:
> > >
> > > Before:
> > > text data bss dec hex filename
> > > 39449 17500 128 57077 def5 ./drivers/gpu/drm/bridge/tc358767.o
> > >
> > > After:
> > > text data bss dec hex filename
> > > 39235 17596 128 56959 de7f ./drivers/gpu/drm/bridge/tc358767.o
> >
> > Why is text smaller and data larger with this change?
>
> There are less instructions being used with the change since it's not
> shoving the array data onto the stack at run time. Instead the array is
> being stored in the data section and there is less object code required
> to access the data.
Ah. It's really because it's not a minimal compilation ala defconfig.
I think you should really stop making these size comparisons with
.config uses that are not based on a defconfig as a whole lot of other
things are going on.
Please notice that the object sizes are significantly smaller below:
So with an x86-64 defconfig and this compilation unit enabled with
CONFIG_OF enabled and CONFIG_DRM_TOSHIBA_TC358767=y, with gcc 10.3
and this change the object size actually increases a bit.
$ size drivers/gpu/drm/bridge/tc358767.o*
text data bss dec hex filename
13554 268 1 13823 35ff drivers/gpu/drm/bridge/tc358767.o.new
13548 268 1 13817 35f9 drivers/gpu/drm/bridge/tc358767.o.old
objdump -h shows these differences:
.old:
0 .text 00001e1f 0000000000000000 0000000000000000 00000040 2**4
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
[...]
14 .rodata 000005ae 0000000000000000 0000000000000000 000046e0 2**5
CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
.new:
0 .text 00001e05 0000000000000000 0000000000000000 00000040 2**4
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
[...]
11 .rodata 000005ce 0000000000000000 0000000000000000 00004600 2**5
CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
cheers, Joe
next prev parent reply other threads:[~2021-08-19 14:40 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-19 13:38 [PATCH] drm/bridge/tc358767: make the array ext_div static const, makes object smaller Colin King
2021-08-19 13:51 ` Joe Perches
2021-08-19 13:54 ` Colin Ian King
2021-08-19 14:40 ` Joe Perches [this message]
2021-08-19 14:51 ` Colin Ian King
2021-08-19 15:10 ` Joe Perches
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