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

["Lange Tang" <lange_tang@163.com>]

At 2026-06-24 15:08:24, "Michael S. Tsirkin" <mst@redhat.com> wrote:
>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.

Thanks for your reply.  I got it, see you next version.
>
>> +	 */
>> +	virtqueue_disable_cb(rq->vq);
>> +
>>  	virtnet_poll_cleantx(rq, budget);
>>  
>>  	received = virtnet_receive(rq, budget, &xdp_xmit);
>> -- 
>> 2.43.0