linux-kernel - Re: [RFC Part2 v1 02/21] genirq: Introduce helper functions to support stacked irq

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Date:	Thu, 18 Sep 2014 14:14:43 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Grant Likely <grant.likely@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Joerg Roedel <joro@...tes.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC Part2 v1 02/21] genirq: Introduce helper functions to support
 stacked irq_chip



On 2014/9/18 4:58, Thomas Gleixner wrote:
> On Wed, 17 Sep 2014, Jiang Liu wrote:
>> On 2014/9/17 1:45, Thomas Gleixner wrote:
>>> On Thu, 11 Sep 2014, Jiang Liu wrote:
>>>> +#ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
>>>> +void irq_chip_ack_parent(struct irq_data *data)
>>>> +{
>>>> +	data = data->parent_data;
>>>> +	if (data && data->chip && data->chip->irq_ack)
>>>> +		data->chip->irq_ack(data);
>>>
>>> Why is this restricted to a single parent level and does not go down
>>> the whole stack?
>> Hi Thomas,
>> 	It happens to work on x86, and we want to achieve a bit
>> performance advantage by not walking down the whole stack.
>> If preferred, I will change it to walk the whole stack.
> 
> Happens to work on my machine is always a bad argument :)
> 
> Now, I can see why you want to do that, but if we do an optimization
> like that then we should really get rid of the conditional.
> 
> You surely need a conditional on data->chip and data->chip->callback
> for a full stackq walk, but for an explicit request to use the parents
> ack the parent better has a chip with an ack function, right?
> 
> void irq_chip_ack_parent(struct irq_data *data)
> {
> 	data = data->parent_data;
> 	data->chip->irq_ack(data);
> }
Sure, will optimize it further as above code.
Regards!
Gerry
> 
> Thanks,
> 
> 	tglx
> 
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