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Date: Wed, 15 Apr 2015 15:24:26 +0200
From: Michal Marek <mmarek@suse.cz>
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To: Alexey Dobriyan <adobriyan@gmail.com>
CC: akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tags: much faster, parallel "make tags"
References: <20150414172047.GA5641@p183.telecom.by>
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On 2015-04-14 19:20, 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@gmail.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)
> +	fi

I wonder if we should rather respect the -j option to make here. But
then most people probably won't realize that make tags is parallel and
will not use -j when generating tags. So let's leave it as is.


> +
> +	rm -f .make-tags.src.* .make-tags.*

.make-tags.src.* is a subset of .make-tags.*


> +
> +	all_target_sources >.make-tags.src
> +	# seems like Useless Use of cat(1) but not really
> +	NR_LINES=$(cat .make-tags.src | wc -l)
> +	NR_LINES=$((($NR_LINES + $NR_CPUS - 1) / $NR_CPUS))
> +
> +	split -a 6 -d -l $NR_LINES .make-tags.src .make-tags.src.
> +
> +	for i in .make-tags.src.*; do
> +		N=$(echo $i | sed -e 's/.*\.//')
> +		# -u: don't sort now, sort later
> +		cat $i | xargs $1 -a -f .make-tags.$N -u	\

xargs <$i $1 ... if you are concerned about uses of cat(1) ;) and the -a
option is not necessary since we are creating the tmp files.


> +	# write header
> +	$1 -f tags /dev/null
> +	# remove header
> +	for i in .make-tags.*; do
> +		sed -i -e '/^!/d' $i
> +	done
> +	sort .make-tags.* >>tags

The hardcoded "tags" filename will break 'make TAGS' when using
exuberant ctags via an 'etags' symlink.

Michal