Re: [dpdk-dev] [PATCH] net/bonding: ensure fairness among slaves

[Matan Azrad <matan@mellanox.com>]

Hi Chas
Please see small comments.

> From: Chas Williams 
> Some PMDs, especially ones with vector receives, require a minimum
> number of receive buffers in order to receive any packets.  If the first slave
> read leaves less than this number available, a read from the next slave may
> return 0 implying that the slave doesn't have any packets which results in
> skipping over that slave as the next active slave.

It is true not only in case of 0.
It makes sense that the first polling slave gets the majority part of the burst while the others just get smaller part
I suggest to rephrase to the general issue . 

> 
> To fix this, implement round robin for the slaves during receive that is only
> advanced to the next slave at the end of each receive burst.
> This should also provide some additional fairness in processing in
> bond_ethdev_rx_burst as well.
> 
> Fixes: 2efb58cbab6e ("bond: new link bonding library")

If it is a fix, why not to use a fix title?
Maybe
net/bonding: fix the slaves Rx fairness 

> Cc: stable@dpdk.org
> 
> Signed-off-by: Chas Williams <chas3@att.com>
Besides that:
Acked-by: Matan Azrad <matan@mellanox.com>

> ---
>  drivers/net/bonding/rte_eth_bond_pmd.c | 50
> ++++++++++++++++++++++------------
>  1 file changed, 32 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/net/bonding/rte_eth_bond_pmd.c
> b/drivers/net/bonding/rte_eth_bond_pmd.c
> index b84f32263..f25faa75c 100644
> --- a/drivers/net/bonding/rte_eth_bond_pmd.c
> +++ b/drivers/net/bonding/rte_eth_bond_pmd.c
> @@ -58,28 +58,33 @@ bond_ethdev_rx_burst(void *queue, struct
> rte_mbuf **bufs, uint16_t nb_pkts)  {
>  	struct bond_dev_private *internals;
> 
> -	uint16_t num_rx_slave = 0;
>  	uint16_t num_rx_total = 0;
> -
> +	uint16_t slave_count;
> +	uint16_t active_slave;
>  	int i;
> 
>  	/* Cast to structure, containing bonded device's port id and queue id
> */
>  	struct bond_rx_queue *bd_rx_q = (struct bond_rx_queue *)queue;
> -
>  	internals = bd_rx_q->dev_private;
> +	slave_count = internals->active_slave_count;
> +	active_slave = internals->active_slave;
> 
> +	for (i = 0; i < slave_count && nb_pkts; i++) {
> +		uint16_t num_rx_slave;
> 
> -	for (i = 0; i < internals->active_slave_count && nb_pkts; i++) {
>  		/* Offset of pointer to *bufs increases as packets are
> received
>  		 * from other slaves */
> -		num_rx_slave = rte_eth_rx_burst(internals-
> >active_slaves[i],
> +		num_rx_slave = rte_eth_rx_burst(
> +				internals->active_slaves[active_slave],
>  				bd_rx_q->queue_id, bufs + num_rx_total,
> nb_pkts);
> -		if (num_rx_slave) {
> -			num_rx_total += num_rx_slave;
> -			nb_pkts -= num_rx_slave;
> -		}
> +		num_rx_total += num_rx_slave;
> +		nb_pkts -= num_rx_slave;
> +		if (++active_slave == slave_count)
> +			active_slave = 0;
>  	}
> 
> +	if (++internals->active_slave == slave_count)
> +		internals->active_slave = 0;
>  	return num_rx_total;
>  }
> 
> @@ -258,25 +263,32 @@ bond_ethdev_rx_burst_8023ad_fast_queue(void
> *queue, struct rte_mbuf **bufs,
>  	uint16_t num_rx_total = 0;	/* Total number of received packets
> */
>  	uint16_t slaves[RTE_MAX_ETHPORTS];
>  	uint16_t slave_count;
> -
> -	uint16_t i, idx;
> +	uint16_t active_slave;
> +	uint16_t i;
> 
>  	/* Copy slave list to protect against slave up/down changes during tx
>  	 * bursting */
>  	slave_count = internals->active_slave_count;
> +	active_slave = internals->active_slave;
>  	memcpy(slaves, internals->active_slaves,
>  			sizeof(internals->active_slaves[0]) * slave_count);
> 
> -	for (i = 0, idx = internals->active_slave;
> -			i < slave_count && num_rx_total < nb_pkts; i++,
> idx++) {
> -		idx = idx % slave_count;
> +	for (i = 0; i < slave_count && nb_pkts; i++) {
> +		uint16_t num_rx_slave;
> 
>  		/* Read packets from this slave */
> -		num_rx_total += rte_eth_rx_burst(slaves[idx], bd_rx_q-
> >queue_id,
> -				&bufs[num_rx_total], nb_pkts -
> num_rx_total);
> +		num_rx_slave = rte_eth_rx_burst(slaves[active_slave],
> +						bd_rx_q->queue_id,
> +						bufs + num_rx_total,
> nb_pkts);
> +		num_rx_total += num_rx_slave;
> +		nb_pkts -= num_rx_slave;
> +
> +		if (++active_slave == slave_count)
> +			active_slave = 0;
>  	}
> 
> -	internals->active_slave = idx;
> +	if (++internals->active_slave == slave_count)
> +		internals->active_slave = 0;
> 
>  	return num_rx_total;
>  }
> @@ -459,7 +471,9 @@ bond_ethdev_rx_burst_8023ad(void *queue, struct
> rte_mbuf **bufs,
>  			idx = 0;
>  	}
> 
> -	internals->active_slave = idx;
> +	if (++internals->active_slave == slave_count)
> +		internals->active_slave = 0;
> +
>  	return num_rx_total;
>  }
> 
> --
> 2.14.4