[PATCH v3] virtio_net: disable cb when NAPI is busy-polled

[PATCH v3] virtio_net: disable cb when NAPI is busy-polled

[Longjun Tang]

From: Longjun Tang <tanglongjun@kylinos.cn>

When busy-poll is active, napi_schedule_prep() returns false in
virtqueue_napi_schedule(), so virtqueue_disable_cb() is skipped.
The device may keep firing irqs until reaches virtqueue_napi_complete().
Under load (received == budget), it will lead to a large number
of spurious interrupts.

Fix it by disabling the callback at the virtnet_poll() entry. This keeps
the callback off while we poll and re-enable by virtqueue_napi_complete()
when going idle.

Fixes: ceef438d613f ("virtio_net: remove custom busy_poll")
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Longjun Tang <tanglongjun@kylinos.cn>

---
V1 -> V2: Remain agnostic to busy polling
V2 -> V3: Add fixes tag
---
 drivers/net/virtio_net.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index f4adcfee7a80..0a11f2b32500 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3008,6 +3008,11 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 	unsigned int xdp_xmit = 0;
 	bool napi_complete;
 
+	/* Keep callbacks suppressed for the duration of this poll,
+	 * busy-poll need.
+	 */
+	virtqueue_disable_cb(rq->vq);
+
 	virtnet_poll_cleantx(rq, budget);
 
 	received = virtnet_receive(rq, budget, &xdp_xmit);
-- 
2.43.0

Re: [PATCH v3] virtio_net: disable cb when NAPI is busy-polled

[Michael S. Tsirkin]

On Wed, Jun 24, 2026 at 03:02:06PM +0800, Longjun Tang wrote:
> From: Longjun Tang <tanglongjun@kylinos.cn>
> 
> When busy-poll is active, napi_schedule_prep() returns false in
> virtqueue_napi_schedule(), so virtqueue_disable_cb() is skipped.
> The device may keep firing irqs until reaches virtqueue_napi_complete().
> Under load (received == budget), it will lead to a large number
> of spurious interrupts.
> 
> Fix it by disabling the callback at the virtnet_poll() entry. This keeps
> the callback off while we poll and re-enable

and it is re-enabled

> by virtqueue_napi_complete()
> when going idle.
> 
> Fixes: ceef438d613f ("virtio_net: remove custom busy_poll")
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Longjun Tang <tanglongjun@kylinos.cn>
> 
> ---
> V1 -> V2: Remain agnostic to busy polling
> V2 -> V3: Add fixes tag
> ---
>  drivers/net/virtio_net.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index f4adcfee7a80..0a11f2b32500 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3008,6 +3008,11 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
>  	unsigned int xdp_xmit = 0;
>  	bool napi_complete;
>  
> +	/* Keep callbacks suppressed for the duration of this poll,
> +	 * busy-poll need.

I don't know what "busy-poll need" means. Just drop this part?
In fact, the whole comment can go, we know virtqueue_disable_cb
disables callbacks.

> +	 */
> +	virtqueue_disable_cb(rq->vq);
> +
>  	virtnet_poll_cleantx(rq, budget);
>  
>  	received = virtnet_receive(rq, budget, &xdp_xmit);
> -- 
> 2.43.0