linux-kernel - Re: [tip:irq/core] x86: Sanitize apb timer interrupt handling

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Message-ID: <20101012154416.000035ad@unknown>
Date:	Tue, 12 Oct 2010 15:44:16 -0700
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	mingo@...e.hu, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:irq/core] x86: Sanitize apb timer interrupt handling

Thomas Gleixner Wed, 13 Oct 2010 00:26:08 +0200 (CEST)
>On Tue, 12 Oct 2010, Jacob Pan wrote:
>
>> Thomas Gleixner Tue, 12 Oct 2010 23:28:19 +0200 (CEST)
>> >On Tue, 12 Oct 2010, Jacob Pan wrote:
>> >
>> >> 
>> >> >x86: Sanitize apb timer interrupt handling
>> >> >
>> >> >Disable the interrupt in CPU_DEAD where it belongs.
>> >> My main concern is the performance cost. The power management code for
>> >> Moorestown system make use of the cpu hotplug code (disable_nonboot_cpus)
>> >> but much more frequently. The system low power states are call S0 idle
>> >> state (s0ix).
>> >> 
>> >> Leaving the irq enabled at the chip and desc level between S0ix states
>> >> might give some performance benefit. That was my original thought.
>> >> Will it cause problems?
>> >
>> >Errm. I merily moved it to the place where it should be. You do the
>> >disable/enable dance already today.
>> >
>> I think I only do disable/enable at the timer HW level today during cpu hp
>> notification, not calling disable_irq(). Am i missing something?
>
>apbt_setup_irq()
>{
> ...
> 
>--->	disable_irq(adev->irq);
>	desc->status |= IRQ_MOVE_PCNTXT;
>	irq_set_affinity(adev->irq, cpumask_of(adev->cpu));
>	/* APB timer irqs are set up as mp_irqs, timer is edge triggerred */
>	set_irq_chip_and_handler_name(adev->irq, chip, handle_edge_irq, "edge");
>--->	enable_irq(adev->irq);
>	if (system_state == SYSTEM_BOOTING)
> ...
>}
>
>So that's a disable/enable pair on every cpu hotplug, right ?
>
>Now I moved the disable to CPU_DEAD where it belongs and the enable
>stayed at the same place.
apbt_setup_irq() does not get called in cpu hotplug code,
but CPU_DEAD notification will happen every time disable_nonboot_cpus()
are called. Since Moorestown OSPM code uses disable_nonboot_cpus often,
that is why i am concerned about the overhead of disable_irq().

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