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