Re: [dpdk-dev] [PATCH v4 3/3] net/af_xdp: fix maximum MTU value

[Ye Xiaolong <xiaolong.ye@intel.com>]

On 02/13, Ciara Loftus wrote:
>The maximum MTU for af_xdp zero copy is equal to the page size less the
>frame overhead introduced by AF_XDP (XDP HR = 256) and DPDK (frame headroom
>= 320). The patch updates this value to reflect this.
>
>This change also makes it possible to remove unneeded constants for both
>zero-copy and copy mode.
>
>Fixes: d8a210774e1d ("net/af_xdp: support unaligned umem chunks")
>Cc: stable@dpdk.org
>
>Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
>---
> drivers/net/af_xdp/rte_eth_af_xdp.c | 23 +++++++++++------------
> 1 file changed, 11 insertions(+), 12 deletions(-)
>
>diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c b/drivers/net/af_xdp/rte_eth_af_xdp.c
>index a0edfc3cd3..06124ba789 100644
>--- a/drivers/net/af_xdp/rte_eth_af_xdp.c
>+++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
>@@ -58,13 +58,6 @@ static int af_xdp_logtype;
> 
> #define ETH_AF_XDP_FRAME_SIZE		2048
> #define ETH_AF_XDP_NUM_BUFFERS		4096
>-#ifdef XDP_UMEM_UNALIGNED_CHUNK_FLAG
>-#define ETH_AF_XDP_MBUF_OVERHEAD	128 /* sizeof(struct rte_mbuf) */
>-#define ETH_AF_XDP_DATA_HEADROOM \
>-	(ETH_AF_XDP_MBUF_OVERHEAD + RTE_PKTMBUF_HEADROOM)
>-#else
>-#define ETH_AF_XDP_DATA_HEADROOM	0
>-#endif
> #define ETH_AF_XDP_DFLT_NUM_DESCS	XSK_RING_CONS__DEFAULT_NUM_DESCS
> #define ETH_AF_XDP_DFLT_START_QUEUE_IDX	0
> #define ETH_AF_XDP_DFLT_QUEUE_COUNT	1
>@@ -601,7 +594,14 @@ eth_dev_info(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
> 	dev_info->max_tx_queues = internals->queue_cnt;
> 
> 	dev_info->min_mtu = RTE_ETHER_MIN_MTU;
>-	dev_info->max_mtu = ETH_AF_XDP_FRAME_SIZE - ETH_AF_XDP_DATA_HEADROOM;
>+#if defined(XDP_UMEM_UNALIGNED_CHUNK_FLAG)
>+	dev_info->max_mtu = getpagesize() -
>+				sizeof(struct rte_mempool_objhdr) -
>+				sizeof(struct rte_mbuf) -
>+				RTE_PKTMBUF_HEADROOM - XDP_PACKET_HEADROOM;
>+#else
>+	dev_info->max_mtu = ETH_AF_XDP_FRAME_SIZE - XDP_PACKET_HEADROOM;
>+#endif
> 
> 	dev_info->default_rxportconf.nb_queues = 1;
> 	dev_info->default_txportconf.nb_queues = 1;
>@@ -803,7 +803,7 @@ xsk_umem_info *xdp_umem_configure(struct pmd_internals *internals,
> 		.fill_size = ETH_AF_XDP_DFLT_NUM_DESCS,
> 		.comp_size = ETH_AF_XDP_DFLT_NUM_DESCS,
> 		.frame_size = ETH_AF_XDP_FRAME_SIZE,
>-		.frame_headroom = ETH_AF_XDP_DATA_HEADROOM };
>+		.frame_headroom = 0 };
> 	char ring_name[RTE_RING_NAMESIZE];
> 	char mz_name[RTE_MEMZONE_NAMESIZE];
> 	int ret;
>@@ -828,8 +828,7 @@ xsk_umem_info *xdp_umem_configure(struct pmd_internals *internals,
> 
> 	for (i = 0; i < ETH_AF_XDP_NUM_BUFFERS; i++)
> 		rte_ring_enqueue(umem->buf_ring,
>-				 (void *)(i * ETH_AF_XDP_FRAME_SIZE +
>-					  ETH_AF_XDP_DATA_HEADROOM));
>+				 (void *)(i * ETH_AF_XDP_FRAME_SIZE));
> 
> 	snprintf(mz_name, sizeof(mz_name), "af_xdp_umem_%s_%u",
> 		       internals->if_name, rxq->xsk_queue_idx);
>@@ -938,7 +937,7 @@ eth_rx_queue_setup(struct rte_eth_dev *dev,
> 	/* Now get the space available for data in the mbuf */
> 	buf_size = rte_pktmbuf_data_room_size(mb_pool) -
> 		RTE_PKTMBUF_HEADROOM;
>-	data_size = ETH_AF_XDP_FRAME_SIZE - ETH_AF_XDP_DATA_HEADROOM;
>+	data_size = ETH_AF_XDP_FRAME_SIZE;
> 
> 	if (data_size > buf_size) {
> 		AF_XDP_LOG(ERR, "%s: %d bytes will not fit in mbuf (%d bytes)\n",
>-- 
>2.17.1
>

Reviewed-by: Xiaolong Ye <xiaolong.ye@intel.com>