linux-kernel - Re: [RFC PATCH 2/2] sched: idle: IRQ based next prediction for idle period

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Date:	Mon, 18 Jan 2016 14:21:53 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	peterz@...radead.org, rafael@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, nicolas.pitre@...aro.org,
	vincent.guittot@...aro.org
Subject: Re: [RFC PATCH 2/2] sched: idle: IRQ based next prediction for idle
 period

On 01/08/2016 04:43 PM, Thomas Gleixner wrote:
> On Wed, 6 Jan 2016, Daniel Lezcano wrote:

[ ... ]

>> +	/*
>> +	 * For all the irq already setup, assign the timing callback.
>> +	 * All interrupts with their desc NULL will be discarded.
>> +	 */
>> +	for_each_irq_desc(irq, desc)
>> +		sched_irq_timing_setup(irq, desc->action);
>
> No, no, no. This belongs into the core code register_irq_timings() function
> which installs the handler into the irq descs with the proper protections and
> once it has done that enables the static key.
>
> The above is completely unprotected against interrupts being setup or even
> freed concurrently.
>
> Aside of that, you call that setup function in setup_irq for each action() and
> here you call it only for the first one.

Hi Thomas,

I went through the different comments and almost finished the changes 
but I think the 'register_ops' approach, which happens after some irq 
were setup, introduces some useless complexity and because of the desc 
lock section, the ops can't do memory allocation. Before going further, 
I am wondering if declaring the irq_timings_ops statically (read without 
'register_ops' - hence without a init time dependency) and calling the 
init/free ops from alloc_desc/free_desc wouldn't be cleaner and simpler.

What do you think ?

   -- Daniel


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