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From: "Skidanov, Alexey" <Alexey.Skidanov@amd.com>
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC: "Gabbay, Oded" <Oded.Gabbay@amd.com>
Subject: CONFIG_PREEMPT_COUNT
Thread-Topic: CONFIG_PREEMPT_COUNT
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Date: Mon, 31 Mar 2014 10:38:12 +0000
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Hello,

I found that preempt_enable() and preempt_disable() macros are defined differently depending on CONFIG_PREEMPT_COUNT:
- They increment per CPU preemption counter, if CONFIG_PREEMPT_COUNT defined
- They do nothing (just call barrier), if not.
I have it undefined in my source tree.

The questions are:
1. What is the purpose of CONFIG_PREEMPT_COUNT define and how I can define it?
2. In the previous kernel versions, spin_lock() and spin_unlock() call preempt_enable() and preempt_disable() respectively, ensuring that the current task will not be preempted by any other task while lock is held. Is this still ensured with these macros defined as "do nothing" ?

Thanks
Alexey