linux-kernel - Re: [PATCH 2/3] kbuild: handle module compression while running 'make modules

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Date:	Wed, 20 Aug 2014 03:25:45 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andi Kleen <andi@...stfloor.org>,
	Bertrand Jacquin <beber@...eeweb.net>
Cc:	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	Willy Tarreau <w@....eu>
Subject: Re: [PATCH 2/3] kbuild: handle module compression while running 'make modules_install'.

Andi Kleen <andi@...stfloor.org> writes:
> Bertrand Jacquin <beber@...eeweb.net> writes:
>>  
>> +# CONFIG_MODULE_COMPRESS, if defined, will cause module to be compressed
>> +# after they are installed in agreement with CONFIG_MODULE_COMPRESS_GZIP
>> +# or CONFIG_MODULE_COMPRESS_XZ.
>> +
>> +mod_compress_cmd = true
>> +ifdef CONFIG_MODULE_COMPRESS
>> +  ifdef CONFIG_MODULE_COMPRESS_GZIP
>> +    mod_compress_cmd = gzip -n -9
>
> Please don't use gzip -9. The gain is very small, but it can make
> the time to compress much longer. Just use plain gzip.

Interesting:

$ time find * -name '*.ko' | xargs -n 1 gzip
real	0m9.404s
user	0m7.283s
sys	0m1.667s
$ du -c `find * -name '*.ko.gz'` | tail -n1
56412	total

time find * -name '*.ko' | xargs -n 1 gzip -9
real	1m1.968s
user	0m58.850s
sys	0m1.786s
$ du -c `find * -name '*.ko.gz'` | tail -n1
55764	total

$ time find * -name '*.ko' | xargs -n 1 xz
real	1m23.396s
user	1m13.893s
sys	0m9.134s
$ du -c `find * -name '*.ko.xz` | tail -n1
46868	total

$ time find * -name '*.ko' | xargs -n 1 xz -9
real	1m47.202s
user	1m25.962s
sys	0m21.298s
$ du -c `find * -name '*.ko.xz` | tail -n1
46868	total

So, Andi is right.  Please skip -9 for both options: it makes little
(.gz) or no (.xz) difference and it slows things down.

Cheers,
Rusty.
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