Re: [dpdk-dev] [PATCH 09/15] net/vmxnet3: switch MSS hint to dynamic mbuf field

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 10/26/20 8:20 AM, Thomas Monjalon wrote:
> The segment count, used for MSS guess,
> was stored in the deprecated mbuf field udata64.
> It is moved to a dynamic field in order to allow removal of udata64.
> 
> Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
> ---
>  drivers/net/vmxnet3/vmxnet3_ethdev.c | 15 +++++++++++++++
>  drivers/net/vmxnet3/vmxnet3_ethdev.h |  2 ++
>  drivers/net/vmxnet3/vmxnet3_rxtx.c   | 10 ++++++----
>  3 files changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/vmxnet3/vmxnet3_ethdev.c b/drivers/net/vmxnet3/vmxnet3_ethdev.c
> index 6920ab568c..eeb1152b61 100644
> --- a/drivers/net/vmxnet3/vmxnet3_ethdev.c
> +++ b/drivers/net/vmxnet3/vmxnet3_ethdev.c
> @@ -59,6 +59,8 @@
>  	 DEV_RX_OFFLOAD_JUMBO_FRAME |   \
>  	 DEV_RX_OFFLOAD_RSS_HASH)
>  
> +int vmxnet3_segs_dynfield_offset;
> +
>  static int eth_vmxnet3_dev_init(struct rte_eth_dev *eth_dev);
>  static int eth_vmxnet3_dev_uninit(struct rte_eth_dev *eth_dev);
>  static int vmxnet3_dev_configure(struct rte_eth_dev *dev);
> @@ -233,6 +235,11 @@ eth_vmxnet3_dev_init(struct rte_eth_dev *eth_dev)
>  	struct vmxnet3_hw *hw = eth_dev->data->dev_private;
>  	uint32_t mac_hi, mac_lo, ver;
>  	struct rte_eth_link link;
> +	static const struct rte_mbuf_dynfield vmxnet3_segs_dynfield_desc = {
> +		.name = "rte_net_vmxnet3_dynfield_segs",
> +		.size = sizeof(uint8_t),
> +		.align = __alignof__(uint8_t),
> +	};
>  
>  	PMD_INIT_FUNC_TRACE();
>  
> @@ -242,6 +249,14 @@ eth_vmxnet3_dev_init(struct rte_eth_dev *eth_dev)
>  	eth_dev->tx_pkt_prepare = vmxnet3_prep_pkts;
>  	pci_dev = RTE_ETH_DEV_TO_PCI(eth_dev);
>  
> +	/* extra mbuf field is required to guess MSS */
> +	vmxnet3_segs_dynfield_offset =
> +		rte_mbuf_dynfield_register(&vmxnet3_segs_dynfield_desc);
> +	if (vmxnet3_segs_dynfield_offset < 0) {
> +		PMD_INIT_LOG(ERR, "Cannot register mbuf field.");
> +		return -rte_errno;
> +	}
> +
>  	/*
>  	 * for secondary processes, we don't initialize any further as primary
>  	 * has already done this work.
> diff --git a/drivers/net/vmxnet3/vmxnet3_ethdev.h b/drivers/net/vmxnet3/vmxnet3_ethdev.h
> index dd685b02b7..5730e94d50 100644
> --- a/drivers/net/vmxnet3/vmxnet3_ethdev.h
> +++ b/drivers/net/vmxnet3/vmxnet3_ethdev.h
> @@ -193,4 +193,6 @@ uint16_t vmxnet3_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
>  uint16_t vmxnet3_prep_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
>  			uint16_t nb_pkts);
>  
> +extern int vmxnet3_segs_dynfield_offset;
> +
>  #endif /* _VMXNET3_ETHDEV_H_ */
> diff --git a/drivers/net/vmxnet3/vmxnet3_rxtx.c b/drivers/net/vmxnet3/vmxnet3_rxtx.c
> index e10f9ee870..6655622f94 100644
> --- a/drivers/net/vmxnet3/vmxnet3_rxtx.c
> +++ b/drivers/net/vmxnet3/vmxnet3_rxtx.c
> @@ -674,6 +674,7 @@ vmxnet3_guess_mss(struct vmxnet3_hw *hw, const Vmxnet3_RxCompDesc *rcd,
>  	struct rte_ipv6_hdr *ipv6_hdr;
>  	struct rte_tcp_hdr *tcp_hdr;
>  	char *ptr;
> +	uint8_t segs;
>  
>  	RTE_ASSERT(rcd->tcp);
>  
> @@ -710,9 +711,9 @@ vmxnet3_guess_mss(struct vmxnet3_hw *hw, const Vmxnet3_RxCompDesc *rcd,
>  	tcp_hdr = (struct rte_tcp_hdr *)(ptr + hlen);
>  	hlen += (tcp_hdr->data_off & 0xf0) >> 2;
>  
> -	if (rxm->udata64 > 1)
> -		return (rte_pktmbuf_pkt_len(rxm) - hlen +
> -				rxm->udata64 - 1) / rxm->udata64;
> +	segs = *RTE_MBUF_DYNFIELD(rxm, vmxnet3_segs_dynfield_offset, uint8_t *);
> +	if (segs > 1)
> +		return (rte_pktmbuf_pkt_len(rxm) - hlen + segs - 1) / segs;
>  	else
>  		return hw->mtu - hlen + sizeof(struct rte_ether_hdr);
>  }
> @@ -737,7 +738,8 @@ vmxnet3_rx_offload(struct vmxnet3_hw *hw, const Vmxnet3_RxCompDesc *rcd,
>  					(const Vmxnet3_RxCompDescExt *)rcd;
>  
>  			rxm->tso_segsz = rcde->mss;
> -			rxm->udata64 = rcde->segCnt;
> +			*RTE_MBUF_DYNFIELD(rxm, vmxnet3_segs_dynfield_offset,
> +					uint8_t *) = rcde->segCnt;
>  			ol_flags |= PKT_RX_LRO;
>  		}
>  	} else { /* Offloads set in eop */
> 

I think it should be a rule of thumb to introduce helper
macro to access a dynamic field (as you do in few of
previous patches).

It should be just nearby declaration of the the offset
variable.