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Date: Mon, 1 Mar 2010 09:56:13 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Linus <torvalds@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>,
       linux-next@vger.kernel.org, Len Brown <lenb@kernel.org>,
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       Rusty Russell <rusty@rustcorp.com.au>,
       Al Viro <viro@ZenIV.linux.org.uk>, J??rn Engel <joern@logfs.org>
Subject: Re: linux-next: current pending merge fix patches
Message-ID: <20100301085613.GA2867@elte.hu>
References: <20100301160445.5e281f11.sfr@canb.auug.org.au>
 <20100301081021.GB8049@elte.hu>
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* Ingo Molnar <mingo@elte.hu> wrote:

> So i'd argue to not backmerge during the merge window (and i have stopped 
> doing that myself a few cycles ago, and it clearly helped things) - but in 
> any case it's certainly no big deal and up to Linus i guess.

What i do instead is that once Linus pulls from me i pull back immediately to 
test, and if it's fine i base further subsystem patches on that and test the 
heck out of the combination from that point on.

That's the collective 'point of no looking back' when subsystem people should 
jump in and help out testing the "final" combination.

But if a subsystem tree backmerges during the merge window any sooner 
(_before_ Linus pulls), it can cause criss-cross merges (as Linus may not pull 
or may pull later during which fixes arrive, etc.), creating a less readable 
history, etc. - which may make integration and problem isolation somewhat 
harder in the end.

( It's not a big deal in isolation and i dont think Linus actually rejects
  trees that do the occasional backmerge - but the combination of many small
  deals can have a bigger effect. )

There are exceptions, such as tricky conflicts that i know to be problematic - 
in that case i occasionally backmerge. But it's relatively rare - 90%+ of the 
conflicts are trivial and all-or-nothing affairs (i.e. if you mess it up the 
kernel wont work very well, so it's immediately noticeable).

Thanks,

	Ingo