From: marc.zyngier@arm•com (Marc Zyngier)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC PATCH v1 2/4] irqchip: GICv3: set non-percpu irqs status with _IRQ_MOVE_PCNTXT
Date: Mon, 07 Sep 2015 15:56:37 +0100 [thread overview]
Message-ID: <55EDA5A5.9070805@arm.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1509071502080.15006@nanos>
Hi Thomas,
On 07/09/15 14:24, Thomas Gleixner wrote:
> On Mon, 7 Sep 2015, Marc Zyngier wrote:
>> On 06/09/15 06:56, Jiang Liu wrote:
>>> On 2015/9/6 12:23, Yang Yingliang wrote:
>>>> Use irq_settings_set_move_pcntxt() helper irqs status with
>>>> _IRQ_MOVE_PCNTXT. So that it can do set affinity when calling
>>>> irq_set_affinity_locked().
>>> Hi Yingliang,
>>> We could only set _IRQ_MOVE_PCNTCT flag to enable migrating
>>> IRQ in process context if your hardware platform supports atomically
>>> change IRQ configuration. Not sure whether that's true for GICv3.
>>> If GICv3 doesn't support atomically change irq configuration, this
>>> change may cause trouble.
>>
>> I think it boils down to what exactly "process context" means here. If
>> this means "we do not need to mask the interrupt" while moving it, then
>> it should be fine (the GIC architecture guarantees that a pending
>> interrupt will be migrated).
>>
>> Is there any other requirement for this flag?
>
> The history of this flag is as follows:
>
> On x86 interrupts can only be safely migrated while the interrupt is
> handled.
Woa! That's creative! :-) I suppose this doesn't work very well with CPU
hotplug though...
> With the introduction of IRQ remapping this requirement
> changed. Remapped interrupts can be migrated in any context.
>
> If you look at irq_set_affinity_locked()
>
> if (irq_can_move_pcntxt(data) {
> irq_do_set_affinity(data,...)
> chip->irq_set_affinity(data,...);
> } else {
> irqd_set_move_pending(data);
> }
>
> So if IRQ_MOVE_PCNTXT is not set, we handle the migration of the
> interrupt from next the interrupt. If it's set set_affinity() is
> called right away.
OK, that is now starting to make more sense.
> All architectures which do not select GENERIC_PENDING_IRQ are using
> the direct method.
Right. On ARM, only the direct method makes sense so far (we have no
constraint such as the one you describe above).
So I wonder why we bother introducing the IRQ_MOVE_PCNTXT flag on ARM at
all. Is that just because migration.c is only compiled when
GENERIC_PENDING_IRQ is set?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2015-09-07 14:56 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-06 4:23 [RFC PATCH v1 0/4] arm/arm64: fix a migrating irq bug when hotplug cpu Yang Yingliang
2015-09-06 4:23 ` [RFC PATCH v1 1/4] genirq: Introduce irq_settings_set_move_pcntxt() helper Yang Yingliang
2015-09-06 22:08 ` Thomas Gleixner
2015-09-07 1:49 ` Yang Yingliang
2015-09-06 4:23 ` [RFC PATCH v1 2/4] irqchip: GICv3: set non-percpu irqs status with _IRQ_MOVE_PCNTXT Yang Yingliang
2015-09-06 5:56 ` Jiang Liu
2015-09-07 2:03 ` Yang Yingliang
2015-09-07 12:32 ` Marc Zyngier
2015-09-07 13:24 ` Thomas Gleixner
2015-09-07 14:56 ` Marc Zyngier [this message]
2015-09-07 14:58 ` Thomas Gleixner
2015-09-07 16:33 ` Jiang Liu
2015-09-06 4:23 ` [RFC PATCH v1 3/4] genirq: rename config GENERIC_PENDING_IRQ to GENERIC_IRQ_MIGRATION Yang Yingliang
2015-09-06 4:23 ` [RFC PATCH v1 4/4] arm/arm64: fix a migrating irq bug when hotplug cpu Yang Yingliang
2015-09-06 5:55 ` Jiang Liu
2015-09-07 2:33 ` Yang Yingliang
2015-09-06 8:07 ` [RFC PATCH v1 0/4] " Jiang Liu
2015-09-07 2:54 ` Yang Yingliang
2015-09-07 1:54 ` Jiang Liu
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