irqchip/sifive-plic: Implement irq_set_affinity() for SMP host
Currently on SMP host, all CPUs take external interrupts routed via PLIC. All CPUs will try to claim a given external interrupt but only one of them will succeed while other CPUs would simply resume whatever they were doing before. This means if we have N CPUs then for every external interrupt N-1 CPUs will always fail to claim it and waste their CPU time. Instead of above, external interrupts should be taken by only one CPU and we should have provision to explicitly specify IRQ affinity from kernel-space or user-space. This patch provides irq_set_affinity() implementation for PLIC driver. It also updates irq_enable() such that PLIC interrupts are only enabled for one of CPUs specified in IRQ affinity mask. With this patch in-place, we can change IRQ affinity at any-time from user-space using procfs. Example: / # cat /proc/interrupts CPU0 CPU1 CPU2 CPU3 8: 44 0 0 0 SiFive PLIC 8 virtio0 10: 48 0 0 0 SiFive PLIC 10 ttyS0 IPI0: 55 663 58 363 Rescheduling interrupts IPI1: 0 1 3 16 Function call interrupts / # / # / # echo 4 > /proc/irq/10/smp_affinity / # / # cat /proc/interrupts CPU0 CPU1 CPU2 CPU3 8: 45 0 0 0 SiFive PLIC 8 virtio0 10: 160 0 17 0 SiFive PLIC 10 ttyS0 IPI0: 68 693 77 410 Rescheduling interrupts IPI1: 0 2 3 16 Function call interrupts Signed-off-by: Anup Patel <anup@brainfault.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
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