linux-kernel - Re: 'git describe' is very slow on development trees with lots of commits

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Date:	Wed, 31 Oct 2012 18:52:26 +0100
From:	Pavel Machek <pavel@....cz>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	David Ahern <dsahern@...il.com>, git@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	linux-kernel@...r.kernel.org, Andrew Vagin <avagin@...nvz.org>,
	Borislav Petkov <bp@...64.org>,
	David Howells <dhowells@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephane Eranian <eranian@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>, arnaldo.melo@...il.com,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: 'git describe' is very slow on development trees with lots of
 commits

Hi!

> (Cc:-ed the Git development list.)
> 
> * David Ahern <dsahern@...il.com> wrote:
> 
> > PERF-VERSION-GEN and specifically the git commands are the 
> > cause of more delay than the config checks, especially when 
> > doing the build in a VM with the kernel source on an NFS 
> > mount.
> 
> Yes, I have noticed that too.
....
> The cost on this pretty fast machine is about 1 msecs per commit 
> - which adds up to about 2.5 seconds during much of the 
> development cycle.

Well... I noticed my builds when little changed are very slow... and
it was due to the computation of version string. Ouch.

pavel@amd:~/mainline-altera/linux$ time git describe
fixes-for-linus-506-g71ca8691
0.68user 0.22system 27.82 (0m27.820s) elapsed 3.26%CPU
pavel@amd:~/mainline-altera/linux$ 

(Cached it is more reasonable 3 seconds, but it keeps going out of
cache all the time. Uncached clean build is 3 minutes, cached is 9
seconds + time to do git describe).

Thikpad X60.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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