linux-kernel - Re: [PATCH v3] tags: much faster, parallel "make tags"

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Message-ID: <20150510132633.GA1717@p183.telecom.by>
Date:	Sun, 10 May 2015 16:26:34 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Pádraig Brady <P@...igBrady.com>
Cc:	akpm@...ux.foundation.org, mmarek@...e.cz,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] tags: much faster, parallel "make tags"

On Sat, May 09, 2015 at 06:07:18AM +0100, Pádraig Brady wrote:
> On 08/05/15 14:26, Alexey Dobriyan wrote:

> >  exuberant()
> >  {
> > -	all_target_sources | xargs $1 -a                        \
> > +	rm -f .make-tags.*
> > +
> > +	all_target_sources >.make-tags.src
> > +	NR_CPUS=$(getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1)
> 
> `nproc` is simpler and available since coreutils 8.1 (2009-11-18)

nproc was discarded because getconf is standartized.

> > +	NR_LINES=$(wc -l <.make-tags.src)
> > +	NR_LINES=$((($NR_LINES + $NR_CPUS - 1) / $NR_CPUS))
> > +
> > +	split -a 6 -d -l $NR_LINES .make-tags.src .make-tags.src.
> 
> `split -d -nl/$(nproc)` is simpler and available since coreutils 8.8 (2010-12-22)

-nl/ can't count and always make first file somewhat bigger, which is
suspicious. What else it can't do right?

> > +	sort .make-tags.* >>$2
> > +	rm -f .make-tags.*
> 
> Using sort --merge would speed up significantly?

By ~1 second, yes.

> Even faster would be to get sort to skip the header lines, avoiding the need for sed.
> It's a bit awkward and was discussed at:
> http://lists.gnu.org/archive/html/coreutils/2013-01/msg00027.html
> Summarising that, is if not using merge you can:
> 
>   tlines=$(($(wc -l < "$2") + 1))
>   tail -q -n+$tlines .make-tags.* | LC_ALL=C sort >>$2
> 
> Or if merge is appropriate then:
> 
>   tlines=$(($(wc -l < "$2") + 1))
>   eval "eval LC_ALL=C sort -m '<(tail -n+$tlines .make-tags.'{1..$(nproc)}')'" >>$2

Might as well teach ctags to do real parallel processing.
LC_* are set by top level Makefile.

> p.p.s. You may want to `trap EXIT cleanup` to rm -f .make-tags.*

The real question is how to kill ctags reliably.
Naive

	trap 'kill $(jobs -p); rm -f .make-tags.*' TERM INT

doesn't work.

Files are removed, but processes aren't.
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