netdev - Re: [PATCH net-next] tsnep: Link queues to NAPIs

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Message-ID: <91fc249e-c11a-47a1-aafe-fef833c3bafa@engleder-embedded.com>
Date: Mon, 13 Jan 2025 21:32:23 +0100
From: Gerhard Engleder <gerhard@...leder-embedded.com>
To: Joe Damato <jdamato@...tly.com>, magnus.karlsson@...el.com
Cc: andrew@...n.ch, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tsnep: Link queues to NAPIs

On 13.01.25 20:59, Joe Damato wrote:
> On Fri, Jan 10, 2025 at 11:39:39PM +0100, Gerhard Engleder wrote:
>> Use netif_queue_set_napi() to link queues to NAPI instances so that they
>> can be queried with netlink.
>>
>> $ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
>>                           --dump queue-get --json='{"ifindex": 11}'
>> [{'id': 0, 'ifindex': 11, 'napi-id': 9, 'type': 'rx'},
>>   {'id': 1, 'ifindex': 11, 'napi-id': 10, 'type': 'rx'},
>>   {'id': 0, 'ifindex': 11, 'napi-id': 9, 'type': 'tx'},
>>   {'id': 1, 'ifindex': 11, 'napi-id': 10, 'type': 'tx'}]
>>
>> Additionally use netif_napi_set_irq() to also provide NAPI interrupt
>> number to userspace.
>>
>> $ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
>>                           --do napi-get --json='{"id": 9}'
>> {'defer-hard-irqs': 0,
>>   'gro-flush-timeout': 0,
>>   'id': 9,
>>   'ifindex': 11,
>>   'irq': 42,
>>   'irq-suspend-timeout': 0}
>>
>> Providing information about queues to userspace makes sense as APIs like
>> XSK provide queue specific access. Also XSK busy polling relies on
>> queues linked to NAPIs.
>>
>> Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>
>> ---
>>   drivers/net/ethernet/engleder/tsnep_main.c | 28 ++++++++++++++++++----
>>   1 file changed, 23 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/engleder/tsnep_main.c b/drivers/net/ethernet/engleder/tsnep_main.c
>> index 45b9f5780902..71e950e023dc 100644
>> --- a/drivers/net/ethernet/engleder/tsnep_main.c
>> +++ b/drivers/net/ethernet/engleder/tsnep_main.c
>> @@ -1984,23 +1984,41 @@ static int tsnep_queue_open(struct tsnep_adapter *adapter,
>>   
>>   static void tsnep_queue_enable(struct tsnep_queue *queue)
>>   {
>> +	struct tsnep_adapter *adapter = queue->adapter;
>> +
>> +	netif_napi_set_irq(&queue->napi, queue->irq);
>>   	napi_enable(&queue->napi);
>> -	tsnep_enable_irq(queue->adapter, queue->irq_mask);
>> +	tsnep_enable_irq(adapter, queue->irq_mask);
>>   
>> -	if (queue->tx)
>> +	if (queue->tx) {
>> +		netif_queue_set_napi(adapter->netdev, queue->tx->queue_index,
>> +				     NETDEV_QUEUE_TYPE_TX, &queue->napi);
>>   		tsnep_tx_enable(queue->tx);
>> +	}
>>   
>> -	if (queue->rx)
>> +	if (queue->rx) {
>> +		netif_queue_set_napi(adapter->netdev, queue->rx->queue_index,
>> +				     NETDEV_QUEUE_TYPE_RX, &queue->napi);
>>   		tsnep_rx_enable(queue->rx);
>> +	}
>>   }
>>   
>>   static void tsnep_queue_disable(struct tsnep_queue *queue)
> A>  {
>> -	if (queue->tx)
>> +	struct tsnep_adapter *adapter = queue->adapter;
>> +
>> +	if (queue->rx)
>> +		netif_queue_set_napi(adapter->netdev, queue->rx->queue_index,
>> +				     NETDEV_QUEUE_TYPE_RX, NULL);
>> +
>> +	if (queue->tx) {
>>   		tsnep_tx_disable(queue->tx, &queue->napi);
>> +		netif_queue_set_napi(adapter->netdev, queue->tx->queue_index,
>> +				     NETDEV_QUEUE_TYPE_TX, NULL);
>> +	}
>>   
>>   	napi_disable(&queue->napi);
>> -	tsnep_disable_irq(queue->adapter, queue->irq_mask);
>> +	tsnep_disable_irq(adapter, queue->irq_mask);
>>   
>>   	/* disable RX after NAPI polling has been disabled, because RX can be
>>   	 * enabled during NAPI polling
> 
> The changes generally look OK to me (it seems RTNL is held on all
> paths where this code can be called from as far as I can tell), but
> there was one thing that stood out to me.
> 
> AFAIU, drivers avoid marking XDP queues as NETDEV_QUEUE_TYPE_RX
> or NETDEV_QUEUE_TYPE_TX. I could be wrong, but that was my
> understanding and I submit patches to several drivers with this
> assumption.
> 
> For example, in commit b65969856d4f ("igc: Link queues to NAPI
> instances"), I unlinked/linked the NAPIs and queue IDs when XDP was
> enabled/disabled. Likewise, in commit 64b62146ba9e ("net/mlx4: link
> NAPI instances to queues and IRQs"), I avoided the XDP queues.
> 
> If drivers are to avoid marking XDP queues as NETDEV_QUEUE_TYPE_RX
> or NETDEV_QUEUE_TYPE_TX, perhaps tsnep needs to be modified
> similarly?

With 5ef44b3cb4 ("xsk: Bring back busy polling support") the linking of
the NAPIs is required for XDP/XSK. So it is strange to me if for XDP/XSK
the NAPIs should be unlinked. But I'm not an expert, so maybe there is
a reason why.

I added Magnus, maybe he knows if XSK queues shall still be linked to
NAPIs.

Gerhard