linux-kernel - Re: IRQ affinity enforced only after first interrupt.

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Date:	Mon, 26 Mar 2012 22:33:29 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Yevgeny Petrilin <yevgenyp@...lanox.co.il>,
	linux-pci@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: IRQ affinity enforced only after first interrupt.

The architecture specific code will determine whether the IRQ could be migrated
in process context. For example, the IRQ_MOVE_PCNTXT flag will be set on x86
systems if interrupt remapping is enabled.

On 03/26/2012 10:28 PM, Bjorn Helgaas wrote:
> [This is not really a PCI question, so +cc Thomas, LKML.]
> 
> On Mon, Mar 26, 2012 at 3:06 AM, Yevgeny Petrilin
> <yevgenyp@...lanox.co.il> wrote:
>> Hello,
>>
>> I'm working on an issue where affinity changes to IRQ only have effect after the first interrupt which still happens on the original core.
>> I understand that the decision regarding it takes place in this code:
>>
>>        if (irq_can_move_pcntxt(data)) {
>>                ret = chip->irq_set_affinity(data, mask, false);
>>                switch (ret) {
>>                case IRQ_SET_MASK_OK:
>>                        cpumask_copy(data->affinity, mask);
>>                case IRQ_SET_MASK_OK_NOCOPY:
>>                        irq_set_thread_affinity(desc);
>>                        ret = 0;
>>                }
>>        } else {
>>                irqd_set_move_pending(data);
>>                irq_copy_pending(desc, mask);
>>        }
>>
>> Which means that the "IRQD_MOVE_PCNTXT" flag is not set in irq_data->state_use_accessors.
>> I was able to add this flag using irq_modify_status(), which is probably not the way to go.
>> This option also doesn't exist in older kernels (2.6.32)
>>
>> So the question is, when irq_desc is created, how is it determined that "IRQD_MOVE_PCNTXT" flag is set?
>>
>> Thanks,
>> Yevgeny
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