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Date: Mon, 07 Sep 2015 15:56:37 +0100 From: Marc Zyngier <marc.zyngier@....com> To: Thomas Gleixner <tglx@...utronix.de>, Yang Yingliang <yangyingliang@...wei.com> CC: Jiang Liu <jiang.liu@...ux.intel.com>, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>, Will Deacon <will.deacon@....com>, Russell King - ARM Linux <linux@....linux.org.uk>, Hanjun Guo <hanjun.guo@...aro.org> Subject: Re: [RFC PATCH v1 2/4] irqchip: GICv3: set non-percpu irqs status with _IRQ_MOVE_PCNTXT 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... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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