Subject: Re: preemption when running in the kernel
From: Robert Love <rml@tech9.net>
To: Ingo Oeser <ioe-lkml@rameria.de>
Cc: Frank Cusack <fcusack@fcusack.com>, linux-kernel@vger.kernel.org
In-Reply-To: <200311081402.07345.ioe-lkml@rameria.de>
References: <20031107040427.A32421@google.com>
	 <200311081402.07345.ioe-lkml@rameria.de>
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Date: Sat, 08 Nov 2003 19:23:05 -0500
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On Sat, 2003-11-08 at 08:01, Ingo Oeser wrote:

> While having preemption disabled or while actually holding a spinlock,
> preemption is disabled.
> 
> Disabling preemption is modifying a count, which must reach 0 again to
> have preemption enabled and trigger an reschedule, if needed.
> 
> Think of it roughly as a "counter of reasons to not preempt". If there
> are no reasons anymore, then we preempt.

Hi, Ingo.

This is an accurate description of 2.6, but Frank said for 2.4.

So, Frank, this is correct for 2.6 or 2.4 with the preempt-kernel patch,
but not a stock 2.4 kernel.  A stock 2.4 kernel will never preempt a
task running inside the kernel.

	Robert Love


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