linux-kernel - Re: [PATCH v2] builddeb: parallelize debug module installation

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Date:	Tue, 28 Apr 2015 12:05:19 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	Riku Voipio <riku.voipio@...aro.org>,
	Chris J Arges <chris.j.arges@...onical.com>
CC:	linux-kbuild <linux-kbuild@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] builddeb: parallelize debug module installation

On 2015-04-28 10:57, Riku Voipio wrote:
> On 27 April 2015 at 19:43, Chris J Arges <chris.j.arges@...onical.com> wrote:
>> When building the dbg package, we use a large 'for module in $(find' loop that
>> can be easily parallelized by using 'find | xargs'. This patch modifies this
>> loop to use the later paradigm.
>>
>> In addition, ensure we add '-n1 -P0' to xargs to run as many processes as
>> possible.
>>
>> Signed-off-by: Chris J Arges <chris.j.arges@...onical.com>
>> ---
>>  scripts/package/builddeb | 15 ++++++++-------
>>  1 file changed, 8 insertions(+), 7 deletions(-)
>>
>> diff --git a/scripts/package/builddeb b/scripts/package/builddeb
>> index 88dbf23..538f829 100755
>> --- a/scripts/package/builddeb
>> +++ b/scripts/package/builddeb
>> @@ -152,16 +152,17 @@ if grep -q '^CONFIG_MODULES=y' $KCONFIG_CONFIG ; then
>>                 rmdir "$tmpdir/lib/modules/$version"
>>         fi
>>         if [ -n "$BUILD_DEBUG" ] ; then
>> -               for module in $(find $tmpdir/lib/modules/ -name *.ko -printf '%P\n'); do
>> -                       module=lib/modules/$module
>> -                       mkdir -p $(dirname $dbg_dir/usr/lib/debug/$module)
>> +               find $tmpdir/lib/modules/ -name *.ko -printf '%P\n' | xargs -n1 -P0 -I {} sh -c '
> 
> I would go with -P`getconf _NPROCESSORS_ONLN`. There can be thousands
> of modules (allmodconfig will make 4500).

Yep. I was thinking about retrieving the value of the make -j argument
somehow, but this is not possible and we certainly do not want to
implement the jobserver protocol in shell :-). So using the number of
processors is a sensible choice. What can be done is to detect whether
the -j option is in MAKEFLAGS and only then use multiple instances.

Michal
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