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From: Jeff King <peff@peff.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luke Lu <git@vicaya.com>,
	Christer Weinigel <christer@weinigel.se>,
	Tom Tobin <korpios@korpios.com>,
	git@vger.kernel.org
Subject: Re: On Tabs and Spaces
Date: Wed, 17 Oct 2007 22:45:53 -0400
Message-ID: <20071018024553.GA5186@coredump.intra.peff.net> (raw)
In-Reply-To: <alpine.LFD.0.999.0710171753020.26902@woody.linux-foundation.org>

On Wed, Oct 17, 2007 at 05:59:27PM -0700, Linus Torvalds wrote:

> It happens. We do de-spacification in the kernel occasionally when it is 
> an annoyance. Usually it shows up in patches, though - exactly because 
> code which adds spaces instead of tabs won't line up correctly in the 
> diff.

You have made this claim several times, and I really don't understand
it. If I have 8 spaces, then a diff line will have either " ", "+", or
"-" followed by 8 spaces. If I use a hard tab, then the tab will end up
only taking up 7 spaces because of the nature of tabs.

This might matter if I'm comparing non-diff code to diff code. But in a
diff, _everything_ is indented by exactly one space, so it all lines up.
Is there something I'm missing?

> So it doesn't matter *which* one you use (all spaces or all tabs) in that 
> sense.

Yes, I agree with that (even with an all-tabs policy, there are still
mangled and incorrect patches that come in -- and the maintainer rejects
or fixes them).

Which was what I was trying to point out with my question (though I was
also curious to hear your answer): all-space versus all-tab is largely a
matter of preference. And that means that people who want git to change
to _their_ preference are just being silly.

> And smaller *is* faster. Do something like this on the kernel:
> 
> 	GIT_PAGER= time git grep sched_fair
> 
> and then do the same thing with the kernel sources blown up by 20% by 
> de-tabification. Guess which one is 20% slower?

I was about to tell you that you're full of it, but there really is a
slowdown:

$ cd linux-2.6
$ GIT_PAGER= time git grep sched_fair >/dev/null
0.34user 0.94system 0:01.30elapsed 98%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+7548minor)pagefaults 0swaps

$ find . -name .git -prune -o -type f | xargs perl -pi -e 's/\t/        /g'
$ git-commit -a -m de-tabify
$ git-repack -a -d
$ GIT_PAGER= time git grep sched_fair >/dev/null
0.42user 1.06system 0:01.54elapsed 96%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+7591minor)pagefaults 0swaps

It's actually about 16%.


Gah, I can't believe I've not only been sucked into a tab vs spaces
discussion, but now I've actually wasted time doing a performance
comparison on it.

As an aside, that commit was enough to trigger a "git-gc --auto", which
was my first experience with it. It's actually kind of annoying
(especially since I was about to repack -a -d).

-Peff

  reply index

Thread overview: 100+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-10-16  6:45 Michael Witten
2007-10-16  7:04 ` Shawn O. Pearce
2007-10-16  7:27   ` Michael Witten
2007-10-16 17:20     ` Andreas Ericsson
2007-10-16 17:40       ` Sam Ravnborg
2007-10-16 23:09         ` Petr Baudis
2007-10-17  3:41           ` David
2007-10-17 11:32             ` Andy Parkins
2007-10-16  8:30 ` Adam Piatyszek
2007-10-16  9:04   ` Lars Hjemli
2007-10-16 10:16     ` Adam Piatyszek
2007-10-16 15:26       ` Jeffrey C. Ollie
2007-10-16 15:51         ` Michael Witten
2007-10-16 17:06           ` Jari Aalto
2007-10-16 19:20             ` Linus Torvalds
2007-10-16 19:36               ` Mike Hommey
2007-10-16 19:47                 ` Linus Torvalds
2007-10-16 19:51                   ` Linus Torvalds
2007-10-16 20:32                   ` Matthieu Moy
2007-10-16 20:18               ` Tom Tobin
2007-10-16 23:05                 ` Linus Torvalds
2007-10-16 23:51                   ` Christer Weinigel
2007-10-17  0:45                     ` Linus Torvalds
2007-10-17  3:08                       ` Michael Witten
2007-10-17  3:29                         ` Linus Torvalds
2007-10-17  7:17                       ` Luke Lu
2007-10-17  9:09                         ` Michael Witten
2007-10-17 10:03                           ` Luke Lu
2007-10-17 10:21                           ` Nikolai Weibull
2007-10-17 11:23                             ` Michael Witten
2007-10-17 22:02                           ` Jari Aalto
2007-10-17 22:36                             ` Andreas Ericsson
2007-10-17 23:38                               ` Jari Aalto
2007-10-18  4:31                                 ` Dmitry Torokhov
2007-10-18  8:19                                   ` Jari Aalto
2007-10-18 11:34                                     ` Petr Baudis
2007-10-18 11:39                                       ` Nikolai Weibull
2007-10-22  3:39                                         ` Miles Bader
2007-10-18  7:15                               ` David Kågedal
2007-10-18  5:42                             ` Mike Hommey
2007-10-18 10:36                               ` Jari Aalto
2007-10-17 15:53                         ` Linus Torvalds
2007-10-17 18:05                           ` Johannes Schindelin
2007-10-17 18:25                           ` Tom Tobin
2007-10-17 18:54                             ` Linus Torvalds
2007-10-17 19:33                               ` Tom Tobin
2007-10-17 19:44                                 ` Linus Torvalds
2007-10-17 19:48                                 ` Nicolas Pitre
2007-10-17 19:52                                 ` Josh England
2007-10-17 19:53                                 ` Linus Torvalds
2007-10-17 21:21                                   ` Christer Weinigel
2007-10-17 22:03                                     ` Linus Torvalds
2007-10-18  6:25                                       ` David Kastrup
2007-10-17 22:11                                     ` Johannes Schindelin
2007-10-17 23:17                                       ` Christer Weinigel
2007-10-17 23:44                                         ` Johannes Schindelin
2007-10-18  0:31                                           ` Christer Weinigel
2007-10-18  6:02                                             ` Andreas Ericsson
2007-10-18  7:12                                             ` David Kågedal
2007-10-17 23:53                                         ` Linus Torvalds
2007-10-17 20:31                                 ` David Kastrup
2007-10-17 21:08                                 ` Johannes Schindelin
2007-10-17 19:47                               ` Jan Wielemaker
2007-10-18  0:32                           ` Jeff King
2007-10-18  0:59                             ` Linus Torvalds
2007-10-18  2:45                               ` Jeff King [this message]
2007-10-18  3:03                                 ` david
2007-10-18  3:00                                   ` Jeff King
2007-10-18  3:32                                     ` Linus Torvalds
2007-10-18  4:17                                       ` Linus Torvalds
2007-10-18  3:13                                 ` Linus Torvalds
2007-10-18  3:23                                   ` Jeff King
2007-10-18  4:41                                     ` [PATCH] Add a message explaining that automatic GC is about to start koreth
2007-10-18  4:44                                       ` Steven Grimm
2007-10-18  5:01                                       ` Jeff King
2007-10-18  5:11                                         ` Shawn O. Pearce
2007-10-18 13:52                                       ` Brian Gernhardt
2007-10-18 14:16                                         ` Steven Grimm
2007-10-18 18:08                                           ` Jeff King
2007-10-19  0:16                                           ` Shawn O. Pearce
2007-10-19  1:12                                             ` [PATCH] git-gc: improve wording of --auto notification Jeff King
2007-10-19  1:24                                               ` Shawn O. Pearce
2007-10-19  1:26                                                 ` Jeff King
2007-10-18 14:21                                         ` [PATCH] Add a message explaining that automatic GC is about to start Nicolas Pitre
2007-10-18  4:52                                 ` On Tabs and Spaces Nicolas Pitre
2007-10-18  4:54                                   ` Jeff King
2007-10-18  4:55                                     ` Jeff King
2007-10-17 16:08                         ` David Kastrup
2007-10-17 17:44                           ` Nicolas Pitre
2007-10-17 19:52                             ` David Kastrup
2007-10-17 17:51                           ` Sean
2007-10-17  5:56                   ` David Kastrup
2007-10-16 20:56               ` Sam Ravnborg
2007-10-18  3:31               ` Paul Wankadia
2007-10-18  4:22                 ` Linus Torvalds
2007-10-18  4:36               ` Dmitry Potapov
2007-10-16 17:23         ` Andreas Ericsson
2007-10-16 18:34           ` Jan-Benedict Glaw
2007-10-16 18:51             ` Andreas Ericsson
2007-10-20 13:54 ` Robin Rosenberg

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