linux-kernel - Re: [RFC PATCH] rcu: don't ignore preempt

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Message-ID: <4B970064.2040802@cn.fujitsu.com>
Date:	Wed, 10 Mar 2010 10:13:56 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	josh@...htriplett.org, LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [RFC PATCH] rcu: don't ignore preempt_disable() in the idle	loop

Paul E. McKenney wrote:
>>
>> This is another try, it uses the fact that idle loops
>> are executing with preept_count()=1.
>> But I didn't look deep into all idle loops.
> 
> Hello, Lai!
> 
> One question below...
> 
> 						Thanx, Paul
> 

[...]

>> +
>> +	if ((preempt_count() & PREEMPT_MASK) > IDLE_CORE_LOOP_PREEMPT_COUNT)
>> +		return 0;
> 
> How does this work in CONFIG_PREEMPT=n kernels?  I don't see how it
> does, regardless of what preempt_count() returns in this case.
> 
>

You are right, It cannot work in CONFIG_PREEMPT=n kernels.
ignore this stupid patch.

Thanx, Lai
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