Subject: Re: [PATCH 4/5] virtio_net: add dedicated XDP transmit queues

From: John Fastabend <[email-masked]>
Date: Fri, 18 Nov 2016 18:43:55 -0800

On 16-11-18 06:10 PM, Jakub Kicinski wrote:
> On Fri, 18 Nov 2016 13:09:53 -0800, Jakub Kicinski wrote:
>> Looks very cool! :)
>>
>> On Fri, 18 Nov 2016 11:00:41 -0800, John Fastabend wrote:
>>> @@ -1542,12 +1546,34 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>>>  		return -EINVAL;
>>>  	}
>>>  
>>> +	curr_qp = vi->curr_queue_pairs - vi->xdp_queue_pairs;
>>> +	if (prog)
>>> +		xdp_qp = num_online_cpus();  
>>
>> Is num_online_cpus() correct here?
> 
> Sorry, I don't know the virto_net code, so I'm probably wrong.  I was
> concerned whether the number of cpus can change but also that the cpu
> mask may be sparse and therefore offsetting by smp_processor_id()
> into the queue table below could bring trouble.
> 

Seem like a valid concerns to me how about num_possible_cpus() instead.

> @@ -353,9 +381,15 @@ static u32 do_xdp_prog(struct virtnet_info *vi,
>  	switch (act) {
>  	case XDP_PASS:
>  		return XDP_PASS;
> +	case XDP_TX:
> +		qp = vi->curr_queue_pairs -
> +			vi->xdp_queue_pairs +
> +			smp_processor_id();
> +		xdp.data = buf + (vi->mergeable_rx_bufs ? 0 : 4);
> +		virtnet_xdp_xmit(vi, qp, &xdp);
> +		return XDP_TX;
>  	default:
>  		bpf_warn_invalid_xdp_action(act);
> -	case XDP_TX:
>  	case XDP_ABORTED:
>  	case XDP_DROP:
>  		return XDP_DROP;
>