linux-kernel - Re: [PATCH 6/7] sched, x86: Provide a per-cpu preempt

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Date:	Tue, 10 Sep 2013 07:02:51 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>, Peter Anvin <hpa@...or.com>,
	Mike Galbraith <bitbucket@...ine.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 6/7] sched, x86: Provide a per-cpu preempt_count
 implementation

On Tue, 2013-09-10 at 15:08 +0200, Peter Zijlstra wrote:

> +static __always_inline int preempt_count(void)
> +{
> +	return __this_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
> +}

Not sure why you used the _4 prefix on all accessors ?

>  
> +#ifdef CONFIG_PREEMPT_COUNT
> +	/*
> +	 * If it were not for PREEMPT_ACTIVE we could guarantee that the
> +	 * preempt_count of all tasks was equal here and this would not be
> +	 * needed.
> +	 */
> +	task_thread_info(prev_p)->saved_preempt_count = __raw_get_cpu_var(__preempt_count);

	this_cpu_read(__preempt_count) ?

> +	__raw_get_cpu_var(__preempt_count) = task_thread_info(next_p)->saved_preempt_count;

	this_cpu_write(__preempt_count,
                       task_thread_info(next_p)->saved_preempt_count;

> +#endif
> +
>  	this_cpu_write(kernel_stack,
>  		  (unsigned long)task_stack_page(next_p) +
>  		  THREAD_SIZE - KERNEL_STACK_OFFSET);
> 
> 


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