From mboxrd@z Thu Jan  1 00:00:00 1970
From: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Subject: Re: A question about (poor) rte_ethdev internal rx/tx
 callbacks design
Date: Mon, 13 Nov 2017 11:39:27 +0100
Message-ID: <20171113103927.GP24849@6wind.com>
References: <2259E047-80C0-40AC-AAF4-F21617605508@gmail.com>
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To: Ilya Matveychikov <matvejchikov@gmail.com>
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On Sat, Nov 11, 2017 at 09:18:45PM +0400, Ilya Matveychikov wrote:
> Folks,
> 
> Are you serious with it:
> 
> typedef uint16_t (*eth_rx_burst_t)(void *rxq,
> 				   struct rte_mbuf **rx_pkts,
> 				   uint16_t nb_pkts);
> typedef uint16_t (*eth_tx_burst_t)(void *txq,
> 				   struct rte_mbuf **tx_pkts,
> 				   uint16_t nb_pkts);
> 
> I’m not surprised that every PMD stores port_id in every and each queue as having just the queue as an argument doesn’t allow to get the device. So the question is - why not to use something like:
> 
> typedef uint16_t (*eth_rx_burst_t)(void *dev, uint16_t queue_id,
> 				   struct rte_mbuf **rx_pkts,
> 				   uint16_t nb_pkts);
> typedef uint16_t (*eth_tx_burst_t)(void *dev, uint16_t queue_id,
> 				   struct rte_mbuf **tx_pkts,
> 				   uint16_t nb_pkts);

I assume it's since the rte_eth_[rt]x_burst() wrappers already pay the price
for that indirection, doing it twice would be redundant.

Basically the cost of storing a back-pointer to dev or a queue index in each
Rx/Tx queue structure is minor compared to saving a couple of CPU cycles
wherever we can.

I'm not saying its the only solution nor the right approach, it's only one
possible explanation for this API.

-- 
Adrien Mazarguil
6WIND