linux-kernel - Re: IS_ENABLED() and non-available symbols

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Date:	Mon, 15 Aug 2011 15:04:40 -0400
From:	Arnaud Lacombe <lacombar@...il.com>
To:	Michal Marek <mmarek@...e.cz>
Cc:	Rabin Vincent <rabin@....in>, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: IS_ENABLED() and non-available symbols

Hi,

On Mon, Aug 15, 2011 at 10:52 AM, Arnaud Lacombe <lacombar@...il.com> wrote:
> [...]
> I'd be interested to also know the cost of all those new symbols on
> build time...
>
here it is; on the parsing itself:

After 1000 iteration of:
% /usr/libexec/gcc/x86_64-redhat-linux/4.5.1/cc1 -E -quiet -v -include
include/generated/autoconf.h /dev/null -o /dev/null -mtune=generic
-march=x86-64 2>/dev/null

x include.before
+ include.after
+--------------------------------------------------------------------------+
| x  x x  x  x x                                  +  + +  +  + +  +  +    +|
||MA_|                                             |_A_|                   |
+--------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x 1000         0.016         0.021         0.016       0.01637 0.00077310911
+ 1000         0.034         0.043         0.035      0.035227 0.00076161083
Difference at 95.0% confidence
        0.018857 +/- 6.7264e-05
        115.192% +/- 0.410898%
        (Student's t, pooled s = 0.000767382)

After 1000 successive build of `init/main.o' (directly calling gcc):

x include.before
+ include.after
+--------------------------------------------------------------------------+
|     xxxxx**++++++                +              +                        |
|     xxxxx***+++++        x      ++       x      +            +           |
|     xxxxx***++*+++ +x+   x  x  x++ x   + x+   ++*  x     x   *           |
|     xxxxx****+*++**+**+*+*x x*xx*++*x++*+**x+ *+* +x *++x*  x*++ +      +|
||____|_A___M_A|_____|                                                     |
+--------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x 1000         0.628         0.835         0.631      0.636217   0.024724466
+ 1000         0.648         0.873         0.651      0.657341   0.026185882
Difference at 95.0% confidence
        0.021124 +/- 0.00223216
        3.32025% +/- 0.350849%
        (Student's t, pooled s = 0.0254657)

Now, an `allyesconfig' take about 5h30 hours to complete on my  Core2
T5670 (capped at 1.2GHz), so this patch would cost an extra 10min.
Still significant, but not too much :-)

 - Arnaud
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