From: Fam Zheng <zhengfei...@bytedance.com> This allows the backend to _not_ trap mmio read of the status register after injecting IRQ in the data path, which can improve the performance significantly by avoiding a vmexit for each interrupt.
More importantly it also makes it possible for Firecracker to hook up virtio-mmio with vhost-net, in which case there isn't a way to implement proper status register handling. For a complete backend that does set either INT_CONFIG bit or INT_VRING bit upon generating irq, what happens hasn't changed. Signed-off-by: Fam Zheng <zhengfei...@bytedance.com> --- drivers/virtio/virtio_mmio.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c index e09edb5c5e06..9b42502b2204 100644 --- a/drivers/virtio/virtio_mmio.c +++ b/drivers/virtio/virtio_mmio.c @@ -295,9 +295,7 @@ static irqreturn_t vm_interrupt(int irq, void *opaque) if (unlikely(status & VIRTIO_MMIO_INT_CONFIG)) { virtio_config_changed(&vm_dev->vdev); ret = IRQ_HANDLED; - } - - if (likely(status & VIRTIO_MMIO_INT_VRING)) { + } else { spin_lock_irqsave(&vm_dev->lock, flags); list_for_each_entry(info, &vm_dev->virtqueues, node) ret |= vring_interrupt(irq, info->vq); -- 2.11.0