linux-kernel - Re: [patch 2.6.24-rc2 1/3] generic gpio -- gpio

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Date:	Wed, 14 Nov 2007 22:28:10 -0800
From:	David Brownell <david-b@...bell.net>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Florian Fainelli <florian.fainelli@...ecomint.eu>,
	Haavard Skinnemoen <hskinnemoen@...el.com>
Subject: Re: [patch 2.6.24-rc2 1/3] generic gpio -- gpio_chip support

On Tuesday 13 November 2007, Nick Piggin wrote:
> > All this does is prevent constant and needless checking for
> > "do you want to preempt me now?" "now?" "now?" in "now?" the
> > middle "now?" of "now?" i/o "now?" loops.
> 
> Actually that's wrong.

Certainly it's right for the mainstream kernel.  Dropping a
lock (other than a raw spinlock) does that checking; when a
loop needs to acquire then drop such a lock, that's exactly
what's going on.

And in the RT kernel, it's got to do the same thing ...
because dropping that lock may mean that a higher priority
task should immediately run and grab the lock.

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