[dpdk-dev] [PATCH v5 2/7] ethdev: allocate max space for internal queue array

[Andrew Rybchenko]

On 10/7/21 2:27 PM, Konstantin Ananyev wrote:
> At queue configure stage always allocate space for maximum possible
> number (RTE_MAX_QUEUES_PER_PORT) of queue pointers.
> That will allow 'fast' inline functions (eth_rx_burst, etc.) to refer
> pointer to internal queue data without extra checking of current number
> of configured queues.
> That would help in future to hide rte_eth_dev and related structures.
> It means that from now on, each ethdev port will always consume:
> ((2*sizeof(uintptr_t))* RTE_MAX_QUEUES_PER_PORT)
> bytes of memory for its queue pointers.
> With RTE_MAX_QUEUES_PER_PORT==1024 (default value) it is 16KB per port.
> 
> Signed-off-by: Konstantin Ananyev <konstantin.ananyev at intel.com>
> ---
>  lib/ethdev/rte_ethdev.c | 36 +++++++++---------------------------
>  1 file changed, 9 insertions(+), 27 deletions(-)
> 
> diff --git a/lib/ethdev/rte_ethdev.c b/lib/ethdev/rte_ethdev.c
> index ed37f8871b..c8abda6dd7 100644
> --- a/lib/ethdev/rte_ethdev.c
> +++ b/lib/ethdev/rte_ethdev.c
> @@ -897,7 +897,8 @@ eth_dev_rx_queue_config(struct rte_eth_dev *dev, uint16_t nb_queues)
>  
>  	if (dev->data->rx_queues == NULL && nb_queues != 0) { /* first time configuration */
>  		dev->data->rx_queues = rte_zmalloc("ethdev->rx_queues",
> -				sizeof(dev->data->rx_queues[0]) * nb_queues,
> +				sizeof(dev->data->rx_queues[0]) *
> +				RTE_MAX_QUEUES_PER_PORT,
>  				RTE_CACHE_LINE_SIZE);

Looking at it I have few questions:
1. Why is nb_queues == 0 case kept as an exception? Yes,
   strictly speaking it is not the problem of the patch,
   DPDK will still segfault (non-debug build) if I
   allocate Tx queues only but call rte_eth_rx_burst().
   After reading the patch description I thought that
   we're trying to address it.
2. Why do we need to allocate memory dynamically?
   Can we just make rx_queues an array of appropriate size?
   May be wasting 512K unconditionally is too much.
3. If wasting 512K is too much, I'd consider to move
   allocation to eth_dev_get(). If

>  		if (dev->data->rx_queues == NULL) {
>  			dev->data->nb_rx_queues = 0;
> @@ -908,21 +909,11 @@ eth_dev_rx_queue_config(struct rte_eth_dev *dev, uint16_t nb_queues)
>  
>  		rxq = dev->data->rx_queues;
>  
> -		for (i = nb_queues; i < old_nb_queues; i++)
> +		for (i = nb_queues; i < old_nb_queues; i++) {
>  			(*dev->dev_ops->rx_queue_release)(rxq[i]);
> -		rxq = rte_realloc(rxq, sizeof(rxq[0]) * nb_queues,
> -				RTE_CACHE_LINE_SIZE);
> -		if (rxq == NULL)
> -			return -(ENOMEM);
> -		if (nb_queues > old_nb_queues) {
> -			uint16_t new_qs = nb_queues - old_nb_queues;
> -
> -			memset(rxq + old_nb_queues, 0,
> -				sizeof(rxq[0]) * new_qs);
> +			rxq[i] = NULL;

It looks like the patch should be rebased on top of
next-net main because of queue release patches.

[snip]