linux-kernel - Re: [PATCH] ide: Fix bug caused by git merge

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Message-ID: <7vr57dfc8x.fsf@alter.siamese.dyndns.org>
Date:	Wed, 01 Jun 2011 14:55:10 -0700
From:	Junio C Hamano <gitster@...ox.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Jens Axboe <jaxboe@...ionio.com>,
	LKML <linux-kernel@...r.kernel.org>, axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] ide: Fix bug caused by git merge

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> Junio - what made it harder for Steven to see the reason may be due
> the default history simplification. I do wonder if we should just make
> "--simplify-merges" the default, because the aggressive and simple
> default culling makes it hard to see merge commits like this that just
> pick one side  over the other. --simplify-merges is more expensive,
> but doesn't have some of the problems the aggressive simplification
> has.

It is more expensive not just in computation cycles but in latency, as it
is inherently a "limited" operation that needs to first walk the history
and then post-process.

  $ time sh -c 'git log drivers/ide/ide-cd.c | head -n 200 >/dev/null'

with and without "--simplify-merges" shows more than 50-fold differences
(0.15s vs 8s).

I am more disturbed by the fact that "git show 698567f3fa7" does not show
the mismerge (even with -c). Of course I know that not showing "taking
from one side" is by design of -c/--cc, but I still feel there should be
something we could do about it.
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