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

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Message-ID: <20150414202450.GA20232@roeck-us.net>
Date:	Tue, 14 Apr 2015 13:24:50 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Randy Dunlap <rdunlap@...radead.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>, mmarek@...e.cz,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tags: much faster, parallel "make tags"

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 ?

Guenter
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