linux-kernel - Re: [PATCH 04/14] init: deps: order network interfaces by link order

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Date:	Sat, 17 Oct 2015 12:03:43 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Alexander Holler <holler@...oftware.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Russell King <linux@....linux.org.uk>,
	Grant Likely <grant.likely@...aro.org>
Subject: Re: [PATCH 04/14] init: deps: order network interfaces by link order

On Sat, Oct 17, 2015 at 11:37 AM, Alexander Holler <holler@...oftware.de> wrote:
>
> Otherwise it's impossible to call initcalls in parallel. I've seen a stable
> topological sort somewhere, but whenever you want to parallelize the
> initcalls, the stable ordering would be gone anyway. So I've decided not to
> look further at a stable topological sort.

So five seconds of googling gave me freely usable source code for a
stable topological sort, that also has a nice reported added
advantage:

 "An interesting property of a stable topological sort is that cyclic
dependencies are tolerated and resolved according to original order of
elements in sequence. This is a desirable feature for many
applications because it allows to sort any sequence with any
imaginable dependencies between the elements"

which seems to be *exactly* what you'd want, especially considering
that right now your patches add extra "no-dependency" markers exactly
because of the cyclical problem.

I think it was the #2 hit on google for "stable topological sort". I
didn't look closely at the source code, but it was not big.

And no, since we don't actually want to parallelize the initcalls
anyway (I had this discussion with you just a month ago), your
objections seem even more questionable. We have separate machinery for
"do this asynchronously", and we want to _keep_ that separate.

                 Linus
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