linux-kernel - Re: kbuild: install to a single directory

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Date:	Mon, 19 Jan 2009 13:18:10 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Sam Ravnborg <sam@...nborg.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: kbuild: install to a single directory


On Monday 2009-01-19 02:24, Sam Ravnborg wrote:
>On Sun, Jan 18, 2009 at 10:17:16PM +0100, Jan Engelhardt wrote:
>> 
>> This proposed change will collect all kernel modules in the
>> single directory, e.g. /lib/modules/2.6.29-rc2/kernel/, without
>> any further directory structure. About 475 inodes (with
>> almost-allmodconfig) less are used, which should result
>> in faster directory traversal (less seeks).
>
>Can you elaborate a little more why this is needed / a good thing.

|[Alan Cox wants the numbers, too]

# File sizes (LZMA'ed RPM payload, but archive contains .ko.gz, so
# it is so-so~~)
-rw-r--r-- 1 31090287 Jan 19 10:51 kernel-2.6.29~rc2.i586.rpm
-rw-r--r-- 1 31031150 Jan 17 23:39 kernel-SingleDir-2.6.29~rc2.i586.rpm

# fs barriers are turned off (got an UPS)
# /tmp is XFS, on a 5400rpm disk on a 2003ish Athlon4 system, 768MB RAM

# installing rpm
md /tmp/test1/var/lib/rpm/;
for ((i = 0; i < 5; ++i)); do
	rm -Rf /tmp/test1/var/lib/rpm/*;
	rpm --root /tmp/test1 --initdb;
	sync; echo 3 >/proc/sys/vm/drop_caches;
	time ( rpm --root /tmp/test1 -ihv kernel-2.6.29~rc2.i586.rpm \
		--nodeps --noscripts; sync; );
done

# kernel-2.6.29~rc2.i586.rpm
real	31.778	33.205	32.076	32.451	33.576
user	6.227	6.274	6.159	6.216	6.290
sys	1.837	1.806	1.888	1.890	1.843

# kernel-SingleDir-2.6.29~rc2.i586.rpm
real	18.666	19.257	19.013	19.257	19.280
user	6.222	6.225	6.232	6.245	6.270
sys	1.900	2.178	2.181	2.183	2.263

# running gzip -d for all .ko.gz
# running depmod
for ((i = 0; i < 5; ++i)); do
	sync; echo 3 >/proc/sys/vm/drop_caches;
	depmod -b /tmp/test1 -r 2.6.29-rc2;
done;

# depmod on kernel
real	32.256	32.242	32.275	32.392	32.529
user	2.004	2.029	2.034	2.051	1.963
sys	0.808	0.842	0.824	0.826	0.847

# depmod on kernel-SingleDir
real	21.062	19.293	19.326	19.411	19.361
user	1.691	1.693	1.660	1.724	1.760
sys	0.761	0.766	0.784	0.767	0.750


>Also:
>-> Is mod-utils compatible with this change

Yes, module-init-tools does not care about the directory layout --
how could it? If it depended such, m-i-t would have to be
adjusted on about every single new subsystem/directory that
is added.

>-> Is userland in general compatible with this change

More so than the .gz stuff, I'd say.
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