linux-kernel - Re: init's children list is long and slows reaping children.

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Date:	Tue, 10 Apr 2007 04:48:54 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Dave Jones <davej@...hat.com>, Robin Holt <holt@....com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Jack Steiner <steiner@...ricas.sgi.com>
Subject: Re: init's children list is long and slows reaping children.

Andrew Morton wrote:
> Well that obviously would be a dumb way to use keventd.  One would need
> to do schedule_work(), kick off the reset then do schedule_delayed_work()
> to wait (or poll) for its termination.

Far too complex.  See what Russell wrote, for instance.

When you are in a kernel thread, you can write more simple, 
straightforward, easy-to-debug code that does

	blah
	msleep()
	blah

rather than creating an insanely complicated state machine for the same 
thing.

ESPECIALLY if you are already inside a state machine (the case with 
libata PIO data xfer), you do not want to add another state machine 
inside of that.

A great many uses of kernel threads are to simplify device reset and 
polling in this way.  I know; a year ago I audited every kernel thread, 
because I was so frustrated with the per-CPU thread explosion.

Thus, rather than forcing authors to make their code more complex, we 
should find another solution.

	Jeff

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