linux-kernel - Re: [patch] drivers: wait for threaded probes between initcall levels

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Date:	Sat, 28 Oct 2006 12:41:50 -0700 (PDT)
From:	Linus Torvalds <torvalds@...l.org>
To:	"Adam J. Richter" <adam@...drasil.com>
cc:	akpm@...l.org, bunk@...sta.de, greg@...ah.com,
	linux-kernel@...r.kernel.org, linux-pci@...ey.karlin.mff.cuni.cz,
	matthew@....cx, pavel@....cz, shemminger@...l.org
Subject: Re: [patch] drivers: wait for threaded probes between initcall levels

On Sat, 28 Oct 2006, Adam J. Richter wrote:

> On Fri, 27 Oct 2006 13:42:44 -0700 (PDT), Linus Torvals wrote:
> >        static struct semaphore outstanding;
> [...]
> >        static void allow_parallel(int n)
> [...]
> >        static void wait_for_parallel(int n)
> [...]
> >        static void execute_in_parallel(int (*fn)(void *), void *arg)
> 
> 	This interface would have problems with nesting.

You miss the point.

They _wouldn't_ be nested.

The "allow_parallel()" and "wait_for_parallel()" calls would be at some 
top-level situation (ie initcalls looping).

Nobody else than the top level would _ever_ use them. Anything under that 
level would just say "I want to do this in parallel" - which is just a 
statement, and has no nesting issues in itself.

The whole notion of "I want to do this in parallel" is basically 
non-nesting. If something is parallel, it's by definition not ordered, and 
thus nesting cannot make sense. All the "ordered" stuff would be either 
done without using "execute_in_parallel()" at all, or it would be ordered 
_within_ one thread that is executed in parallel.

		Linus
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