[PATCH] net/tap: allow more that 4 queues

[Ferruh Yigit]

On 2/29/2024 5:56 PM, Stephen Hemminger wrote:
> The tap device needs to exchange file descriptors for tx and rx.
> But the EAL MP layer has limit of 8 file descriptors per message.
> The ideal resolution would be to increase the number of file
> descriptors allowed for rte_mp_sendmsg(), but this would break
> the ABI. Workaround the constraint by breaking into multiple messages.
> 
> Do not hide errors about MP message failures.
> 
> Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
> ---
>  drivers/net/tap/rte_eth_tap.c | 40 +++++++++++++++++++++++++++++------
>  1 file changed, 33 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
> index 69d9da695bed..df18c328f498 100644
> --- a/drivers/net/tap/rte_eth_tap.c
> +++ b/drivers/net/tap/rte_eth_tap.c
> @@ -863,21 +863,44 @@ tap_mp_req_on_rxtx(struct rte_eth_dev *dev)
>  		msg.fds[fd_iterator++] = process_private->txq_fds[i];
>  		msg.num_fds++;
>  		request_param->txq_count++;
> +
> +		/* Need to break request into chunks */
> +		if (fd_iterator >= RTE_MP_MAX_FD_NUM) {
> +			err = rte_mp_sendmsg(&msg);
> +			if (err < 0)
> +				goto fail;
> +
> +			fd_iterator = 0;
> +			msg.num_fds = 0;
> +			request_param->txq_count = 0;
> +		}
>  	}
>  	for (i = 0; i < dev->data->nb_rx_queues; i++) {
>  		msg.fds[fd_iterator++] = process_private->rxq_fds[i];
>  		msg.num_fds++;
>  		request_param->rxq_count++;
> +
> +		if (fd_iterator >= RTE_MP_MAX_FD_NUM) {
> +			err = rte_mp_sendmsg(&msg);
> +			if (err < 0)
> +				goto fail;
> +
> +			fd_iterator = 0;
> +			msg.num_fds = 0;
> +			request_param->rxq_count = 0;
> +		}
>  	}

Hi Stephen,

Did you able to verify with more than 4 queues?

As far as I can see, in the secondary counterpart of the
'rte_mp_sendmsg()', each time secondary index starts from 0, and
subsequent calls overwrites the fds in secondary.
So practically still only 4 queues works.