ibmvnic: Increase max subcrq indirect entries with fallback

POWER8 support a maximum of 16 subcrq indirect descriptor entries per
H_SEND_SUB_CRQ_INDIRECT call, while POWER9 and newer hypervisors
support up to 128 entries. Increasing the max number of indirect
descriptor entries improves batching efficiency and reduces
hcall overhead, which enhances throughput under large workload on POWER9+.

Currently, ibmvnic driver always uses a fixed number of max indirect
descriptor entries (16). send_subcrq_indirect() treats all hypervisor
errors the same:
- Cleanup and Drop the entire batch of descriptors.
- Return an error to the caller.
- Rely on TCP/IP retransmissions to recover.
- If the hypervisor returns H_PARAMETER (e.g., because 128
entries are not supported on POWER8), the driver will continue
to drop batches, resulting in unnecessary packet loss.

In this patch:
Raise the default maximum indirect entries to 128 to improve ibmvnic
batching on morden platform. But also gracefully fall back to
16 entries for Power 8 systems.

Since there is no VIO interface to query the hypervisor’s supported
limit, vnic handles send_subcrq_indirect() H_PARAMETER errors:
- On first H_PARAMETER failure, log the failure context
- Reduce max_indirect_entries to 16 and allow the single batch to drop.
- Subsequent calls automatically use the correct lower limit,
avoiding repeated drops.

The goal is to optimizes performance on modern systems while handles
falling back for older POWER8 hypervisors.

Performance shows 40% improvements with MTU (1500) on largework load.

Signed-off-by: Mingming Cao <[e-mail]>
Reviewed-by: Brian King <[e-mail]>
Reviewed-by: Haren Myneni <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

drivers/net/ethernet/ibm/ibmvnic.c

···
 		adapter->rx_pool[i].active = 0;
 }
 
+static void ibmvnic_set_safe_max_ind_descs(struct ibmvnic_adapter *adapter)
+{
+	if (adapter->cur_max_ind_descs > IBMVNIC_SAFE_IND_DESC) {
+		netdev_info(adapter->netdev,
+			    "set max ind descs from %u to safe limit %u\n",
+			    adapter->cur_max_ind_descs,
+			    IBMVNIC_SAFE_IND_DESC);
+		adapter->cur_max_ind_descs = IBMVNIC_SAFE_IND_DESC;
+	}
+}
+
 static void replenish_rx_pool(struct ibmvnic_adapter *adapter,
 			      struct ibmvnic_rx_pool *pool)
 {
···
 		sub_crq->rx_add.len = cpu_to_be32(pool->buff_size << shift);
 
 		/* if send_subcrq_indirect queue is full, flush to VIOS */
-		if (ind_bufp->index == IBMVNIC_MAX_IND_DESCS ||
+		if (ind_bufp->index == adapter->cur_max_ind_descs ||
 		    i == count - 1) {
 			lpar_rc =
 				send_subcrq_indirect(adapter, handle,
···
 failure:
 	if (lpar_rc != H_PARAMETER && lpar_rc != H_CLOSED)
 		dev_err_ratelimited(dev, "rx: replenish packet buffer failed\n");
+
+	/* Detect platform limit H_PARAMETER */
+	if (lpar_rc == H_PARAMETER)
+		ibmvnic_set_safe_max_ind_descs(adapter);
+
+	/* For all error case, temporarily drop only this batch
+	 * Rely on TCP/IP retransmissions to retry and recover
+	 */
 	for (i = ind_bufp->index - 1; i >= 0; --i) {
 		struct ibmvnic_rx_buff *rx_buff;
 
···
 		rc = send_subcrq_direct(adapter, handle,
 					(u64 *)ind_bufp->indir_arr);
 
-	if (rc)
+	if (rc) {
+		dev_err_ratelimited(&adapter->vdev->dev,
+				    "tx_flush failed, rc=%u (%llu entries dma=%pad handle=%llx)\n",
+				    rc, entries, &dma_addr, handle);
+		/* Detect platform limit H_PARAMETER */
+		if (rc == H_PARAMETER)
+			ibmvnic_set_safe_max_ind_descs(adapter);
+
+		/* For all error case, temporarily drop only this batch
+		 * Rely on TCP/IP retransmissions to retry and recover
+		 */
 		ibmvnic_tx_scrq_clean_buffer(adapter, tx_scrq);
-	else
+	} else {
 		ind_bufp->index = 0;
+	}
 	return rc;
 }
 
 static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
 {
 	struct ibmvnic_adapter *adapter = netdev_priv(netdev);
+	u32 cur_max_ind_descs = adapter->cur_max_ind_descs;
 	int queue_num = skb_get_queue_mapping(skb);
 	u8 *hdrs = (u8 *)&adapter->tx_rx_desc_req;
 	struct device *dev = &adapter->vdev->dev;
···
 	tx_crq.v1.n_crq_elem = num_entries;
 	tx_buff->num_entries = num_entries;
 	/* flush buffer if current entry can not fit */
-	if (num_entries + ind_bufp->index > IBMVNIC_MAX_IND_DESCS) {
+	if (num_entries + ind_bufp->index > cur_max_ind_descs) {
 		lpar_rc = ibmvnic_tx_scrq_flush(adapter, tx_scrq, true);
 		if (lpar_rc != H_SUCCESS)
 			goto tx_flush_err;
···
 	ind_bufp->index += num_entries;
 	if (__netdev_tx_sent_queue(txq, skb->len,
 				   netdev_xmit_more() &&
-				   ind_bufp->index < IBMVNIC_MAX_IND_DESCS)) {
+				   ind_bufp->index < cur_max_ind_descs)) {
 		lpar_rc = ibmvnic_tx_scrq_flush(adapter, tx_scrq, true);
 		if (lpar_rc != H_SUCCESS)
 			goto tx_err;
···
 	}
 
 	dma_free_coherent(dev,
-			  IBMVNIC_IND_ARR_SZ,
+			  IBMVNIC_IND_MAX_ARR_SZ,
 			  scrq->ind_buf.indir_arr,
 			  scrq->ind_buf.indir_dma);
 
···
 
 	scrq->ind_buf.indir_arr =
 		dma_alloc_coherent(dev,
-				   IBMVNIC_IND_ARR_SZ,
+				   IBMVNIC_IND_MAX_ARR_SZ,
 				   &scrq->ind_buf.indir_dma,
 				   GFP_KERNEL);
 
···
 			rc = reset_sub_crq_queues(adapter);
 		}
 	} else {
+		if (adapter->reset_reason == VNIC_RESET_MOBILITY) {
+			/* After an LPM, reset the max number of indirect
+			 * subcrq descriptors per H_SEND_SUB_CRQ_INDIRECT
+			 * hcall to the default max (e.g POWER8 -> POWER10)
+			 *
+			 * If the new destination platform does not support
+			 * the higher limit max (e.g. POWER10-> POWER8 LPM)
+			 * H_PARAMETER will trigger automatic fallback to the
+			 * safe minimum limit.
+			 */
+			adapter->cur_max_ind_descs = IBMVNIC_MAX_IND_DESCS;
+		}
+
 		rc = init_sub_crqs(adapter);
 	}
 
···
 
 	adapter->wait_for_reset = false;
 	adapter->last_reset_time = jiffies;
+	adapter->cur_max_ind_descs = IBMVNIC_MAX_IND_DESCS;
 
 	rc = register_netdev(netdev);
 	if (rc) {

drivers/net/ethernet/ibm/ibmvnic.h

···
 #define IBMVNIC_BUFFS_PER_POOL	100
 #define IBMVNIC_MAX_QUEUES	16
 #define IBMVNIC_MAX_QUEUE_SZ   4096
-#define IBMVNIC_MAX_IND_DESCS  16
-#define IBMVNIC_IND_ARR_SZ	(IBMVNIC_MAX_IND_DESCS * 32)
+#define IBMVNIC_MAX_IND_DESCS 128
+#define IBMVNIC_SAFE_IND_DESC 16
+#define IBMVNIC_IND_MAX_ARR_SZ (IBMVNIC_MAX_IND_DESCS * 32)
 
 #define IBMVNIC_TSO_BUF_SZ	65536
 #define IBMVNIC_TSO_BUFS	64
···
 	struct ibmvnic_control_ip_offload_buffer ip_offload_ctrl;
 	dma_addr_t ip_offload_ctrl_tok;
 	u32 msg_enable;
+	u32 cur_max_ind_descs;
 
 	/* Vital Product Data (VPD) */
 	struct ibmvnic_vpd *vpd;