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Re: [Xen-devel] [PATCH 1/4] xen/arm: gic: Ensure we have an ISB between ack and do_IRQ()

Hello Julien,

On 19.11.18 18:42, Julien Grall wrote:
There are no issue about processing IRQs before the syncs. It is the same as if an IRQ was raised from ila different pCPUs.
So why do you need that?

From my understanding of gic-vgic code (old vgic), for the IRQs targeting the `current` vcpu, it leads to a faster processing under interrupts storm conditions. If it was all LRs set on previous switch to a guest, a the IRQ will have a chance to go directly to LR instead of setting on lr_pending queue. Also inflight_irqs queue have a chance to be shorter to insert.

Moreover, maybe you can explain me, what's the point of interrupts enabling before for `do_IRQ()` call? Those interrupts would be grabbed and processed anyway, during run through the loop in `gic_interrupt()`. So I see the only outcome of interrupts enabling - spending more time for context switches.

Andrii Anisov.

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