Re: [RFC net-next v2 2/2] igc: Link queues to NAPI instances

[Joe Damato <jdamato@fastly.com>]

On Tue, Oct 15, 2024 at 12:27:01PM +0200, Kurt Kanzenbach wrote:
> On Mon Oct 14 2024, Joe Damato wrote:

[...]

> > diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> > index 7964bbedb16c..59c00acfa0ed 100644
> > --- a/drivers/net/ethernet/intel/igc/igc_main.c
> > +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> > @@ -4948,6 +4948,47 @@ static int igc_sw_init(struct igc_adapter *adapter)
> >  	return 0;
> >  }
> >  
> > +void igc_set_queue_napi(struct igc_adapter *adapter, int q_idx,
> > +			struct napi_struct *napi)
> > +{
> > +	if (adapter->flags & IGC_FLAG_QUEUE_PAIRS) {
> > +		netif_queue_set_napi(adapter->netdev, q_idx,
> > +				     NETDEV_QUEUE_TYPE_RX, napi);
> > +		netif_queue_set_napi(adapter->netdev, q_idx,
> > +				     NETDEV_QUEUE_TYPE_TX, napi);
> > +	} else {
> > +		if (q_idx < adapter->num_rx_queues) {
> > +			netif_queue_set_napi(adapter->netdev, q_idx,
> > +					     NETDEV_QUEUE_TYPE_RX, napi);
> > +		} else {
> > +			q_idx -= adapter->num_rx_queues;
> > +			netif_queue_set_napi(adapter->netdev, q_idx,
> > +					     NETDEV_QUEUE_TYPE_TX, napi);
> > +		}
> > +	}
> > +}
> 
> In addition, to what Vinicius said. I think this can be done
> simpler. Something like this?
> 
> void igc_set_queue_napi(struct igc_adapter *adapter, int vector,
> 			struct napi_struct *napi)
> {
> 	struct igc_q_vector *q_vector = adapter->q_vector[vector];
> 
> 	if (q_vector->rx.ring)
> 		netif_queue_set_napi(adapter->netdev, vector, NETDEV_QUEUE_TYPE_RX, napi);
> 
> 	if (q_vector->tx.ring)
> 		netif_queue_set_napi(adapter->netdev, vector, NETDEV_QUEUE_TYPE_TX, napi);
> }

I tried this suggestion but this does not result in correct output
in the case where IGC_FLAG_QUEUE_PAIRS is disabled.

The output from netlink:

$ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
                             --dump queue-get --json='{"ifindex": 2}'

[{'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'rx'},
 {'id': 1, 'ifindex': 2, 'napi-id': 8194, 'type': 'rx'},
 {'id': 0, 'ifindex': 2, 'type': 'tx'},
 {'id': 1, 'ifindex': 2, 'type': 'tx'}]

Note the lack of a napi-id for the TX queues. This typically happens
when the linking is not done correctly; netif_queue_set_napi should
take a queue id as the second parameter.

I believe the suggested code above should be modified to be as
follows to use ring->queue_index:

  if (q_vector->rx.ring)
    netif_queue_set_napi(adapter->netdev,
                         q_vector->rx.ring->queue_index,
                         NETDEV_QUEUE_TYPE_RX, napi);
  
  if (q_vector->tx.ring)
    netif_queue_set_napi(adapter->netdev,
                         q_vector->tx.ring->queue_index,
                         NETDEV_QUEUE_TYPE_TX, napi);

Which produces correct output:

$ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
                             --dump queue-get --json='{"ifindex": 2}'
[{'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'rx'},
 {'id': 1, 'ifindex': 2, 'napi-id': 8194, 'type': 'rx'},
 {'id': 0, 'ifindex': 2, 'napi-id': 8195, 'type': 'tx'},
 {'id': 1, 'ifindex': 2, 'napi-id': 8196, 'type': 'tx'}]

I wanted to send you a note about this before I post the v3 so that
if/when you review it you'll have the context as to why the v3 code
is slightly different than what was suggested.