linux-kernel - Re: [PATCH] tags: much faster, parallel "make tags"

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Date:	Wed, 15 Apr 2015 11:36:50 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	Guenter Roeck <linux@...ck-us.net>,
	Randy Dunlap <rdunlap@...radead.org>
CC:	Alexey Dobriyan <adobriyan@...il.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tags: much faster, parallel "make tags"

On 2015-04-14 22:24, Guenter Roeck wrote:
> On Tue, Apr 14, 2015 at 01:05:09PM -0700, Randy Dunlap wrote:
>> On 04/14/15 10:20, Alexey Dobriyan wrote:
>>> ctags is single-threaded program. Split list of files to be tagged into
>>> equal parts, 1 part for each CPU and then merge the results.
>>>
>>> Speedup on one 2-way box I have is ~143 s => ~99 s (-31%).
>>> On another 4-way box: ~120 s => ~65 s (-46%!).
>>>
>>> Resulting "tags" files aren't byte-for-byte identical because ctags
>>> program numbers anon struct and enum declarations with "__anonNNN"
>>> symbols. If those lines are removed, "tags" file becomes byte-for-byte
>>> identical with those generated with current code.
>>>
>>> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
>>> ---
>>>
>>>  scripts/tags.sh |   34 ++++++++++++++++++++++++++++++++--
>>>  1 file changed, 32 insertions(+), 2 deletions(-)
>>>
>>> --- a/scripts/tags.sh
>>> +++ b/scripts/tags.sh
>>> @@ -152,7 +152,24 @@ dogtags()
>>>  
>>>  exuberant()
>>>  {
>>> -	all_target_sources | xargs $1 -a                        \
>>> +	NR_CPUS=1
>>> +	if [ -e /proc/cpuinfo ]; then
>>> +		NR_CPUS=$(grep -e '^processor	: ' /proc/cpuinfo | wc -l)
>>
>> That grep is rather arch-specific. If an arch does not have that string
>> (with an embedded tab), won't NR_CPUS be zero?  so at least, set it back to 1?
>>
>> or (if 'getconf' is installed):
>> NR_CPUS = `getconf _NPROCESSORS_ONLN`
>>
> What is wrong with nproc ?

It's too new. 'getconf _NPROCESSORS_ONLN' has been available since 1996
according to glibc.git.

Michal
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