On Fri, Jul 19, 2019 at 09:31:34PM +0800, Fei Li wrote:
> From: Fam Zheng <[email protected]>
>
> 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 <[email protected]>
This has a side effect of skipping vring callbacks
if they trigger at the same time with a config
interrupt.
I don't see why this is safe.
> ---
> 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
