Messages in this thread | | | Date | Mon, 07 Sep 2015 15:56:37 +0100 | From | Marc Zyngier <> | 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...
| |