linux-kernel - Re: [PATCH] wireless: iwlegacy: make const array static to shink object code size Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit

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Message-ID: <alpine.DEB.2.20.1709221252430.3170@hadrien>
Date:   Fri, 22 Sep 2017 12:54:14 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Joe Perches <joe@...ches.com>
cc:     Colin Ian King <colin.king@...onical.com>,
        Stanislaw Gruszka <sgruszka@...hat.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] wireless: iwlegacy: make const array static to shink
 object code size Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding:
 8bit



On Fri, 22 Sep 2017, Joe Perches wrote:

> On Fri, 2017-09-22 at 12:06 +0200, Julia Lawall wrote:
> >
> > On Fri, 22 Sep 2017, Colin Ian King wrote:
> >
> > > On 22/09/17 11:03, Joe Perches wrote:
> > > > On Fri, 2017-09-22 at 09:23 +0200, Julia Lawall wrote:
> > > > >
> > > > > On Thu, 21 Sep 2017, Colin King wrote:
> > > > >
> > > > > > From: Colin Ian King <colin.king@...onical.com>
> > > > > >
> > > > > > Don't populate const array ac_to_fifo on the stack in an inlined
> > > > > > function, instead make it static.  Makes the object code smaller
> > > > > > by over 800 bytes:
> > > > > >
> > > > > >    text	   data	    bss	    dec	    hex	filename
> > > > > >  159029	  33154	   1216	 193399	  2f377	4965-mac.o
> > > > > >
> > > > > >    text	   data	    bss	    dec	    hex	filename
> > > > > >  158122	  33250	   1216	 192588	  2f04c	4965-mac.o
> > > > > >
> > > > > > (gcc version 7.2.0 x86_64)
> > > > >
> > > > > Gcc 7 must be much more aggressive about inlining than gcc 4.  Here is the
> > > > > change that I got on this file:
> > > > >
> > > > >      text          data     bss     dec     hex filename
> > > > > -   76346          1494     152   77992   130a8 drivers/net/wireless/intel/iwlegacy/4965-mac.o
> > > > > +   76298          1494     152   77944   13078 drivers/net/wireless/intel/iwlegacy/4965-mac.o
> > > > > decrease of 48
> > > >
> > > > More likely different CONFIG options.
> > > >
> > > > e.g. allyesconfig vs defconfig with wireless
> > > >
> > >
> > > yup, I used allyesconfig
> >
> > Mine is also allyesconfig.
>
> Odd.
>
> Here is what I get: (Sorry, no gcc-7)
>
> gcc4: gcc-4.9 (Ubuntu 4.9.4-2ubuntu1) 4.9.4
> gcc5: gcc-5 (Ubuntu 5.4.1-8ubuntu1) 5.4.1 20170304
> gcc6: gcc-6 (Ubuntu 6.3.0-12ubuntu2) 6.3.0 20170406
>
> $ size drivers/net/wireless/intel/iwlegacy/4965-mac.o*
>    text	   data	    bss	    dec	    hex	filename
>  118559	   1766	    152	 120477	  1d69d	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc4.allyesconfig.new
>  118623	   1766	    152	 120541	  1d6dd	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc4.allyesconfig.old

My gcc is 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04.3)

You get a savings of 64 and I got a savings of 48, but it's not that big a
difference, compared to what the later versions give.

julia

>   51595	   1156	      0	  52751	   ce0f	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc4.defconfig.new
>   51659	   1156	      0	  52815	   ce4f	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc4.defconfig.old
>  141956	  29790	   1216	 172962	  2a3a2	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc5.allyesconfig.new
>  142671	  29702	   1216	 173589	  2a615	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc5.allyesconfig.old
>   51733	   1156	      0	  52889	   ce99	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc5.defconfig.new
>   51813	   1156	      0	  52969	   cee9	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc5.defconfig.old
>  152991	  29790	   1216	 183997	  2cebd	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc6.allyesconfig.new
>  153722	  29702	   1216	 184640	  2d140	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc6.allyesconfig.old
>   51813	   1156	      0	  52969	   cee9	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc6.defconfig.new
>   51893	   1156	      0	  53049	   cf39	drivers/net/wireless/intel/iwlegacy/4965-mac.o.gcc6.defconfig.old
>
>
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