[PATCH] um: Migrate vector drivers to NAPI

[Johannes Berg]

On Fri, 2022-01-21 at 08:55 +0000, anton.ivanov at cambridgegreys.com
wrote:
> From: Anton Ivanov <anton.ivanov at cambridgegreys.com>
> 
> Migrate UML vector drivers from a bespoke scheduling mechanism
> to NAPI.

Nice :)

> -static void vector_rx(struct vector_private *vp)
> -{
> -	int err;
> -	int iter = 0;
> -
> -	if ((vp->options & VECTOR_RX) > 0)
> -		while (((err = vector_mmsg_rx(vp)) > 0) && (iter < MAX_ITERATIONS))

You can remove the MAX_ITERATIONS define now.


> +static int vector_poll(struct napi_struct *napi, int budget)
>  {
> -	struct vector_private *vp = from_tasklet(vp, t, tx_poll);
> +	struct vector_private *vp = container_of(napi, struct vector_private, napi);
> +	int work_done = 0;
> +	int err;
> +	bool tx_enqueued = false;
>  
> -	vp->estats.tx_kicks++;
> -	vector_send(vp->tx_queue);
> +	if ((vp->options & VECTOR_TX) != 0)
> +		tx_enqueued = (vector_send(vp->tx_queue) > 0);
> +	if ((vp->options & VECTOR_RX) > 0)
> +		err = vector_mmsg_rx(vp);
> +	else {
> +		err = vector_legacy_rx(vp);

It feels like you should honour the NAPI and pass the budget down, using
it to limit the number of packets processed for TX/RX, something like

tx_enqueued = vector_send(..., budget);
budget -= tx_enqueued;

if (budget > 0)
	err = vector_mmsg_rx(vp, budget);

etc.

> @@ -1264,6 +1251,10 @@ static int vector_net_open(struct net_device *dev)
>  		if (vp->header_txbuffer == NULL)
>  			goto out_close;
>  	}
> +	/* NAPI */
> +

That comment feels a bit pointless, but whatever :)

> +	netif_napi_add(vp->dev, &vp->napi, vector_poll, 64);
> +	napi_enable(&vp->napi);

I think this should only be done once when you create the netdev?


> @@ -1312,9 +1303,11 @@ static int vector_net_open(struct net_device *dev)
>  	 * SIGIOs never arrive, and the net never works.
>  	 */
>  
> -	vector_rx(vp);
>  
>  	vector_reset_stats(vp);
> +
> +	napi_schedule(&vp->napi);
> 

The comment should probably move with this?

johannes