[dpdk-dev] [PATCH v5 25/25] mlx5: resurrect Rx scatter support

[Nelio Laranjeiro <nelio.laranjeiro@6wind.com>]

This commit brings back Rx scatter and related support by the MTU update
function. The maximum number of segments per packet is not a fixed value
anymore (previously MLX5_PMD_SGE_WR_N, set to 4 by default) as it caused
performance issues when fewer segments were actually needed as well as
limitations on the maximum packet size that could be received with the
default mbuf size (supporting at most 8576 bytes).

These limitations are now lifted as the number of SGEs is derived from the
MTU (which implies MRU) at queue initialization and during MTU update.

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Signed-off-by: Vasily Philipov <vasilyf@mellanox.com>
Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
---
 drivers/net/mlx5/mlx5_ethdev.c |  90 ++++++++++++++++++++++----
 drivers/net/mlx5/mlx5_rxq.c    |  77 ++++++++++++++++++-----
 drivers/net/mlx5/mlx5_rxtx.c   | 139 ++++++++++++++++++++++++-----------------
 drivers/net/mlx5/mlx5_rxtx.h   |   1 +
 4 files changed, 225 insertions(+), 82 deletions(-)

diff --git a/drivers/net/mlx5/mlx5_ethdev.c b/drivers/net/mlx5/mlx5_ethdev.c
index 698a50e..72f0826 100644
--- a/drivers/net/mlx5/mlx5_ethdev.c
+++ b/drivers/net/mlx5/mlx5_ethdev.c
@@ -725,6 +725,9 @@ mlx5_dev_set_mtu(struct rte_eth_dev *dev, uint16_t mtu)
 	unsigned int i;
 	uint16_t (*rx_func)(void *, struct rte_mbuf **, uint16_t) =
 		mlx5_rx_burst;
+	unsigned int max_frame_len;
+	int rehash;
+	int restart = priv->started;
 
 	if (mlx5_is_secondary())
 		return -E_RTE_SECONDARY;
@@ -738,7 +741,6 @@ mlx5_dev_set_mtu(struct rte_eth_dev *dev, uint16_t mtu)
 		goto out;
 	} else
 		DEBUG("adapter port %u MTU set to %u", priv->port, mtu);
-	priv->mtu = mtu;
 	/* Temporarily replace RX handler with a fake one, assuming it has not
 	 * been copied elsewhere. */
 	dev->rx_pkt_burst = removed_rx_burst;
@@ -746,28 +748,94 @@ mlx5_dev_set_mtu(struct rte_eth_dev *dev, uint16_t mtu)
 	 * removed_rx_burst() instead. */
 	rte_wmb();
 	usleep(1000);
+	/* MTU does not include header and CRC. */
+	max_frame_len = ETHER_HDR_LEN + mtu + ETHER_CRC_LEN;
+	/* Check if at least one queue is going to need a SGE update. */
+	for (i = 0; i != priv->rxqs_n; ++i) {
+		struct rxq *rxq = (*priv->rxqs)[i];
+		unsigned int mb_len;
+		unsigned int size = RTE_PKTMBUF_HEADROOM + max_frame_len;
+		unsigned int sges_n;
+
+		if (rxq == NULL)
+			continue;
+		mb_len = rte_pktmbuf_data_room_size(rxq->mp);
+		assert(mb_len >= RTE_PKTMBUF_HEADROOM);
+		/*
+		 * Determine the number of SGEs needed for a full packet
+		 * and round it to the next power of two.
+		 */
+		sges_n = log2above((size / mb_len) + !!(size % mb_len));
+		if (sges_n != rxq->sges_n)
+			break;
+	}
+	/*
+	 * If all queues have the right number of SGEs, a simple rehash
+	 * of their buffers is enough, otherwise SGE information can only
+	 * be updated in a queue by recreating it. All resources that depend
+	 * on queues (flows, indirection tables) must be recreated as well in
+	 * that case.
+	 */
+	rehash = (i == priv->rxqs_n);
+	if (!rehash) {
+		/* Clean up everything as with mlx5_dev_stop(). */
+		priv_special_flow_disable_all(priv);
+		priv_mac_addrs_disable(priv);
+		priv_destroy_hash_rxqs(priv);
+		priv_fdir_disable(priv);
+		priv_dev_interrupt_handler_uninstall(priv, dev);
+	}
+recover:
 	/* Reconfigure each RX queue. */
 	for (i = 0; (i != priv->rxqs_n); ++i) {
 		struct rxq *rxq = (*priv->rxqs)[i];
-		unsigned int mb_len;
-		unsigned int max_frame_len;
+		struct rxq_ctrl *rxq_ctrl =
+			container_of(rxq, struct rxq_ctrl, rxq);
 		int sp;
+		unsigned int mb_len;
+		unsigned int tmp;
 
 		if (rxq == NULL)
 			continue;
-		/* Calculate new maximum frame length according to MTU and
-		 * toggle scattered support (sp) if necessary. */
-		max_frame_len = (priv->mtu + ETHER_HDR_LEN +
-				 (ETHER_MAX_VLAN_FRAME_LEN - ETHER_MAX_LEN));
 		mb_len = rte_pktmbuf_data_room_size(rxq->mp);
 		assert(mb_len >= RTE_PKTMBUF_HEADROOM);
+		/* Toggle scattered support (sp) if necessary. */
 		sp = (max_frame_len > (mb_len - RTE_PKTMBUF_HEADROOM));
-		if (sp) {
-			ERROR("%p: RX scatter is not supported", (void *)dev);
-			ret = ENOTSUP;
-			goto out;
+		/* Provide new values to rxq_setup(). */
+		dev->data->dev_conf.rxmode.jumbo_frame = sp;
+		dev->data->dev_conf.rxmode.max_rx_pkt_len = max_frame_len;
+		if (rehash)
+			ret = rxq_rehash(dev, rxq_ctrl);
+		else
+			ret = rxq_ctrl_setup(dev, rxq_ctrl, rxq->elts_n,
+					     rxq_ctrl->socket, NULL, rxq->mp);
+		if (!ret)
+			continue;
+		/* Attempt to roll back in case of error. */
+		tmp = (mb_len << rxq->sges_n) - RTE_PKTMBUF_HEADROOM;
+		if (max_frame_len != tmp) {
+			max_frame_len = tmp;
+			goto recover;
 		}
+		/* Double fault, disable RX. */
+		break;
+	}
+	/*
+	 * Use a safe RX burst function in case of error, otherwise mimic
+	 * mlx5_dev_start().
+	 */
+	if (ret) {
+		ERROR("unable to reconfigure RX queues, RX disabled");
+		rx_func = removed_rx_burst;
+	} else if (restart &&
+		 !rehash &&
+		 !priv_create_hash_rxqs(priv) &&
+		 !priv_rehash_flows(priv)) {
+		if (dev->data->dev_conf.fdir_conf.mode == RTE_FDIR_MODE_NONE)
+			priv_fdir_enable(priv);
+		priv_dev_interrupt_handler_install(priv, dev);
 	}
+	priv->mtu = mtu;
 	/* Burst functions can now be called again. */
 	rte_wmb();
 	dev->rx_pkt_burst = rx_func;
diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
index b2ddd0d..908fd0f 100644
--- a/drivers/net/mlx5/mlx5_rxq.c
+++ b/drivers/net/mlx5/mlx5_rxq.c
@@ -644,10 +644,11 @@ static int
 rxq_alloc_elts(struct rxq_ctrl *rxq_ctrl, unsigned int elts_n,
 	       struct rte_mbuf *(*pool)[])
 {
+	const unsigned int sges_n = 1 << rxq_ctrl->rxq.sges_n;
 	unsigned int i;
 	int ret = 0;
 
-	/* For each WR (packet). */
+	/* Iterate on segments. */
 	for (i = 0; (i != elts_n); ++i) {
 		struct rte_mbuf *buf;
 		volatile struct mlx5_wqe_data_seg *scat =
@@ -672,6 +673,9 @@ rxq_alloc_elts(struct rxq_ctrl *rxq_ctrl, unsigned int elts_n,
 		assert(rte_pktmbuf_data_len(buf) == 0);
 		assert(rte_pktmbuf_pkt_len(buf) == 0);
 		assert(!buf->next);
+		/* Only the first segment keeps headroom. */
+		if (i % sges_n)
+			SET_DATA_OFF(buf, 0);
 		PORT(buf) = rxq_ctrl->rxq.port_id;
 		DATA_LEN(buf) = rte_pktmbuf_tailroom(buf);
 		PKT_LEN(buf) = DATA_LEN(buf);
@@ -685,8 +689,8 @@ rxq_alloc_elts(struct rxq_ctrl *rxq_ctrl, unsigned int elts_n,
 		};
 		(*rxq_ctrl->rxq.elts)[i] = buf;
 	}
-	DEBUG("%p: allocated and configured %u single-segment WRs",
-	      (void *)rxq_ctrl, elts_n);
+	DEBUG("%p: allocated and configured %u segments (max %u packets)",
+	      (void *)rxq_ctrl, elts_n, elts_n / (1 << rxq_ctrl->rxq.sges_n));
 	assert(ret == 0);
 	return 0;
 error:
@@ -804,7 +808,9 @@ rxq_rehash(struct rte_eth_dev *dev, struct rxq_ctrl *rxq_ctrl)
 	struct ibv_exp_wq_attr mod;
 	int err;
 
-	DEBUG("%p: rehashing queue %p", (void *)dev, (void *)rxq_ctrl);
+	DEBUG("%p: rehashing queue %p with %u SGE(s) per packet",
+	      (void *)dev, (void *)rxq_ctrl, 1 << rxq_ctrl->rxq.sges_n);
+	assert(!(elts_n % (1 << rxq_ctrl->rxq.sges_n)));
 	/* From now on, any failure will render the queue unusable.
 	 * Reinitialize WQ. */
 	mod = (struct ibv_exp_wq_attr){
@@ -837,7 +843,7 @@ rxq_rehash(struct rte_eth_dev *dev, struct rxq_ctrl *rxq_ctrl)
 		goto error;
 	}
 	/* Update doorbell counter. */
-	rxq_ctrl->rxq.rq_ci = elts_n;
+	rxq_ctrl->rxq.rq_ci = elts_n >> rxq_ctrl->rxq.sges_n;
 	rte_wmb();
 	*rxq_ctrl->rxq.rq_db = htonl(rxq_ctrl->rxq.rq_ci);
 error:
@@ -933,9 +939,42 @@ rxq_ctrl_setup(struct rte_eth_dev *dev, struct rxq_ctrl *rxq_ctrl,
 	int ret = 0;
 
 	(void)conf; /* Thresholds configuration (ignored). */
-	if (desc == 0) {
-		ERROR("%p: invalid number of RX descriptors (must be a"
-		      " multiple of 2)", (void *)dev);
+	/* Enable scattered packets support for this queue if necessary. */
+	assert(mb_len >= RTE_PKTMBUF_HEADROOM);
+	if ((dev->data->dev_conf.rxmode.jumbo_frame) &&
+	    (dev->data->dev_conf.rxmode.max_rx_pkt_len >
+	     (mb_len - RTE_PKTMBUF_HEADROOM))) {
+		unsigned int size =
+			RTE_PKTMBUF_HEADROOM +
+			dev->data->dev_conf.rxmode.max_rx_pkt_len;
+		unsigned int sges_n;
+
+		/*
+		 * Determine the number of SGEs needed for a full packet
+		 * and round it to the next power of two.
+		 */
+		sges_n = log2above((size / mb_len) + !!(size % mb_len));
+		tmpl.rxq.sges_n = sges_n;
+		/* Make sure rxq.sges_n did not overflow. */
+		size = mb_len * (1 << tmpl.rxq.sges_n);
+		size -= RTE_PKTMBUF_HEADROOM;
+		if (size < dev->data->dev_conf.rxmode.max_rx_pkt_len) {
+			ERROR("%p: too many SGEs (%u) needed to handle"
+			      " requested maximum packet size %u",
+			      (void *)dev,
+			      1 << sges_n,
+			      dev->data->dev_conf.rxmode.max_rx_pkt_len);
+			return EOVERFLOW;
+		}
+	}
+	DEBUG("%p: maximum number of segments per packet: %u",
+	      (void *)dev, 1 << tmpl.rxq.sges_n);
+	if (desc % (1 << tmpl.rxq.sges_n)) {
+		ERROR("%p: number of RX queue descriptors (%u) is not a"
+		      " multiple of SGEs per packet (%u)",
+		      (void *)dev,
+		      desc,
+		      1 << tmpl.rxq.sges_n);
 		return EINVAL;
 	}
 	/* Toggle RX checksum offload if hardware supports it. */
@@ -944,7 +983,6 @@ rxq_ctrl_setup(struct rte_eth_dev *dev, struct rxq_ctrl *rxq_ctrl,
 	if (priv->hw_csum_l2tun)
 		tmpl.rxq.csum_l2tun =
 			!!dev->data->dev_conf.rxmode.hw_ip_checksum;
-	(void)mb_len; /* I'll be back! */
 	/* Use the entire RX mempool as the memory region. */
 	tmpl.mr = mlx5_mp2mr(priv->pd, mp);
 	if (tmpl.mr == NULL) {
@@ -994,11 +1032,9 @@ rxq_ctrl_setup(struct rte_eth_dev *dev, struct rxq_ctrl *rxq_ctrl,
 		.wq_context = NULL, /* Could be useful in the future. */
 		.wq_type = IBV_EXP_WQT_RQ,
 		/* Max number of outstanding WRs. */
-		.max_recv_wr = ((priv->device_attr.max_qp_wr < (int)desc) ?
-				priv->device_attr.max_qp_wr :
-				(int)desc),
+		.max_recv_wr = desc >> tmpl.rxq.sges_n,
 		/* Max number of scatter/gather elements in a WR. */
-		.max_recv_sge = 1,
+		.max_recv_sge = 1 << tmpl.rxq.sges_n,
 		.pd = priv->pd,
 		.cq = tmpl.cq,
 		.comp_mask =
@@ -1050,6 +1086,19 @@ rxq_ctrl_setup(struct rte_eth_dev *dev, struct rxq_ctrl *rxq_ctrl,
 		      (void *)dev, strerror(ret));
 		goto error;
 	}
+	/*
+	 * Make sure number of WRs*SGEs match expectations since a queue
+	 * cannot allocate more than "desc" buffers.
+	 */
+	if (((int)attr.wq.max_recv_wr != (desc >> tmpl.rxq.sges_n)) ||
+	    ((int)attr.wq.max_recv_sge != (1 << tmpl.rxq.sges_n))) {
+		ERROR("%p: requested %u*%u but got %u*%u WRs*SGEs",
+		      (void *)dev,
+		      (desc >> tmpl.rxq.sges_n), (1 << tmpl.rxq.sges_n),
+		      attr.wq.max_recv_wr, attr.wq.max_recv_sge);
+		ret = EINVAL;
+		goto error;
+	}
 	/* Save port ID. */
 	tmpl.rxq.port_id = dev->data->port_id;
 	DEBUG("%p: RTE port ID: %u", (void *)rxq_ctrl, tmpl.rxq.port_id);
@@ -1118,7 +1167,7 @@ rxq_ctrl_setup(struct rte_eth_dev *dev, struct rxq_ctrl *rxq_ctrl,
 	tmpl.rxq.elts = elts;
 	*rxq_ctrl = tmpl;
 	/* Update doorbell counter. */
-	rxq_ctrl->rxq.rq_ci = desc;
+	rxq_ctrl->rxq.rq_ci = desc >> rxq_ctrl->rxq.sges_n;
 	rte_wmb();
 	*rxq_ctrl->rxq.rq_db = htonl(rxq_ctrl->rxq.rq_ci);
 	DEBUG("%p: rxq updated with %p", (void *)rxq_ctrl, (void *)&tmpl);
diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
index 8b67949..d944075 100644
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -1548,98 +1548,123 @@ uint16_t
 mlx5_rx_burst(void *dpdk_rxq, struct rte_mbuf **pkts, uint16_t pkts_n)
 {
 	struct rxq *rxq = dpdk_rxq;
-	unsigned int pkts_ret = 0;
-	unsigned int i;
-	unsigned int rq_ci = rxq->rq_ci;
-	const unsigned int elts_n = rxq->elts_n;
-	const unsigned int wqe_cnt = elts_n - 1;
+	const unsigned int wqe_cnt = rxq->elts_n - 1;
 	const unsigned int cqe_cnt = rxq->cqe_n - 1;
+	const unsigned int sges_n = rxq->sges_n;
+	struct rte_mbuf *pkt = NULL;
+	struct rte_mbuf *seg = NULL;
+	volatile struct mlx5_cqe64 *cqe =
+		&(*rxq->cqes)[rxq->cq_ci & cqe_cnt].cqe64;
+	unsigned int i = 0;
+	unsigned int rq_ci = rxq->rq_ci << sges_n;
+	int len;
 
-	for (i = 0; (i != pkts_n); ++i) {
+	while (pkts_n) {
 		unsigned int idx = rq_ci & wqe_cnt;
-		int len;
-		struct rte_mbuf *rep;
-		struct rte_mbuf *pkt;
 		volatile struct mlx5_wqe_data_seg *wqe = &(*rxq->wqes)[idx];
-		volatile struct mlx5_cqe64 *cqe =
-			&(*rxq->cqes)[rxq->cq_ci & cqe_cnt].cqe64;
+		struct rte_mbuf *rep = (*rxq->elts)[idx];
 
-		pkt = (*rxq->elts)[idx];
+		if (pkt)
+			NEXT(seg) = rep;
+		seg = rep;
+		rte_prefetch0(seg);
 		rte_prefetch0(cqe);
+		rte_prefetch0(wqe);
 		rep = rte_mbuf_raw_alloc(rxq->mp);
 		if (unlikely(rep == NULL)) {
+			while (pkt) {
+				seg = NEXT(pkt);
+				rte_mbuf_refcnt_set(pkt, 0);
+				__rte_mbuf_raw_free(pkt);
+				pkt = seg;
+			}
 			++rxq->stats.rx_nombuf;
 			break;
 		}
-		SET_DATA_OFF(rep, RTE_PKTMBUF_HEADROOM);
-		NB_SEGS(rep) = 1;
-		PORT(rep) = rxq->port_id;
-		NEXT(rep) = NULL;
-		len = mlx5_rx_poll_len(rxq, cqe, cqe_cnt);
-		if (unlikely(len == 0)) {
-			rte_mbuf_refcnt_set(rep, 0);
-			__rte_mbuf_raw_free(rep);
-			break;
-		}
-		if (unlikely(len == -1)) {
-			/* RX error, packet is likely too large. */
-			rte_mbuf_refcnt_set(rep, 0);
-			__rte_mbuf_raw_free(rep);
-			++rxq->stats.idropped;
-			--i;
-			goto skip;
+		if (!pkt) {
+			cqe = &(*rxq->cqes)[rxq->cq_ci & cqe_cnt].cqe64;
+			len = mlx5_rx_poll_len(rxq, cqe, cqe_cnt);
+			if (len == 0) {
+				rte_mbuf_refcnt_set(rep, 0);
+				__rte_mbuf_raw_free(rep);
+				break;
+			}
+			if (unlikely(len == -1)) {
+				/* RX error, packet is likely too large. */
+				rte_mbuf_refcnt_set(rep, 0);
+				__rte_mbuf_raw_free(rep);
+				++rxq->stats.idropped;
+				goto skip;
+			}
+			pkt = seg;
+			assert(len >= (rxq->crc_present << 2));
+			/* Update packet information. */
+			if (rxq->csum | rxq->csum_l2tun | rxq->vlan_strip |
+			    rxq->crc_present) {
+				if (rxq->csum) {
+					pkt->packet_type =
+						rxq_cq_to_pkt_type(cqe);
+					pkt->ol_flags =
+						rxq_cq_to_ol_flags(rxq, cqe);
+				}
+				if (cqe->l4_hdr_type_etc &
+				    MLX5_CQE_VLAN_STRIPPED) {
+					pkt->ol_flags |= PKT_RX_VLAN_PKT;
+					pkt->vlan_tci = ntohs(cqe->vlan_info);
+				}
+				if (rxq->crc_present)
+					len -= ETHER_CRC_LEN;
+			}
+			PKT_LEN(pkt) = len;
 		}
+		DATA_LEN(rep) = DATA_LEN(seg);
+		PKT_LEN(rep) = PKT_LEN(seg);
+		SET_DATA_OFF(rep, DATA_OFF(seg));
+		NB_SEGS(rep) = NB_SEGS(seg);
+		PORT(rep) = PORT(seg);
+		NEXT(rep) = NULL;
+		(*rxq->elts)[idx] = rep;
 		/*
 		 * Fill NIC descriptor with the new buffer.  The lkey and size
 		 * of the buffers are already known, only the buffer address
 		 * changes.
 		 */
-		wqe->addr = htonll((uintptr_t)rep->buf_addr +
-				   RTE_PKTMBUF_HEADROOM);
-		(*rxq->elts)[idx] = rep;
-		/* Update pkt information. */
-		if (rxq->csum | rxq->csum_l2tun | rxq->vlan_strip |
-		    rxq->crc_present) {
-			if (rxq->csum) {
-				pkt->packet_type = rxq_cq_to_pkt_type(cqe);
-				pkt->ol_flags = rxq_cq_to_ol_flags(rxq, cqe);
-			}
-			if (cqe->l4_hdr_type_etc & MLX5_CQE_VLAN_STRIPPED) {
-				pkt->ol_flags |= PKT_RX_VLAN_PKT;
-				pkt->vlan_tci = ntohs(cqe->vlan_info);
-			}
-			if (rxq->crc_present)
-				len -= ETHER_CRC_LEN;
+		wqe->addr = htonll(rte_pktmbuf_mtod(rep, uintptr_t));
+		if (len > DATA_LEN(seg)) {
+			len -= DATA_LEN(seg);
+			++NB_SEGS(pkt);
+			++rq_ci;
+			continue;
 		}
-		PKT_LEN(pkt) = len;
-		DATA_LEN(pkt) = len;
+		DATA_LEN(seg) = len;
 #ifdef MLX5_PMD_SOFT_COUNTERS
 		/* Increment bytes counter. */
-		rxq->stats.ibytes += len;
+		rxq->stats.ibytes += PKT_LEN(pkt);
 #endif
 		/* Return packet. */
 		*(pkts++) = pkt;
-		++pkts_ret;
+		pkt = NULL;
+		--pkts_n;
+		++i;
 skip:
+		/* Align consumer index to the next stride. */
+		rq_ci >>= sges_n;
 		++rq_ci;
+		rq_ci <<= sges_n;
 	}
-	if (unlikely((i == 0) && (rq_ci == rxq->rq_ci)))
+	if (unlikely((i == 0) && ((rq_ci >> sges_n) == rxq->rq_ci)))
 		return 0;
-	/* Repost WRs. */
-#ifdef DEBUG_RECV
-	DEBUG("%p: reposting %u WRs", (void *)rxq, i);
-#endif
 	/* Update the consumer index. */
-	rxq->rq_ci = rq_ci;
+	rxq->rq_ci = rq_ci >> sges_n;
 	rte_wmb();
 	*rxq->cq_db = htonl(rxq->cq_ci);
 	rte_wmb();
 	*rxq->rq_db = htonl(rxq->rq_ci);
 #ifdef MLX5_PMD_SOFT_COUNTERS
 	/* Increment packets counter. */
-	rxq->stats.ipackets += pkts_ret;
+	rxq->stats.ipackets += i;
 #endif
-	return pkts_ret;
+	return i;
 }
 
 /**
diff --git a/drivers/net/mlx5/mlx5_rxtx.h b/drivers/net/mlx5/mlx5_rxtx.h
index 41605f9..f6e2cba 100644
--- a/drivers/net/mlx5/mlx5_rxtx.h
+++ b/drivers/net/mlx5/mlx5_rxtx.h
@@ -106,6 +106,7 @@ struct rxq {
 	unsigned int csum_l2tun:1; /* Same for L2 tunnels. */
 	unsigned int vlan_strip:1; /* Enable VLAN stripping. */
 	unsigned int crc_present:1; /* CRC must be subtracted. */
+	unsigned int sges_n:2; /* Log 2 of SGEs (max buffers per packet). */
 	uint16_t rq_ci;
 	uint16_t cq_ci;
 	uint16_t elts_n;
-- 
2.1.4