net/sfc: correct estimation of max DMA descriptors required

Previous too pessimistic estimation made completely impossible to send
packets with many segments (more than 100 with minimum Tx ring size).

Fixes: 8b00f426eb66 ("net/sfc: implement EF10 native Tx datapath")

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andrew Lee <alee@solarflare.com>

diff --git a/drivers/net/sfc/sfc_ef10_tx.c b/drivers/net/sfc/sfc_ef10_tx.c
index 74bd822..bac9baa 100644 (file)
--- a/drivers/net/sfc/sfc_ef10_tx.c
+++ b/drivers/net/sfc/sfc_ef10_tx.c
@@ -47,19 +47,10 @@
 #define sfc_ef10_tx_err(dpq, ...) \
        SFC_DP_LOG(SFC_KVARG_DATAPATH_EF10, ERR, dpq, __VA_ARGS__)
 
-/** Maximum length of the mbuf segment data */
-#define SFC_MBUF_SEG_LEN_MAX \
-       ((1u << (8 * sizeof(((struct rte_mbuf *)0)->data_len))) - 1)
-
 /** Maximum length of the DMA descriptor data */
 #define SFC_EF10_TX_DMA_DESC_LEN_MAX \
        ((1u << ESF_DZ_TX_KER_BYTE_CNT_WIDTH) - 1)
 
-/** Maximum number of DMA descriptors per mbuf segment */
-#define SFC_EF10_TX_MBUF_SEG_DESCS_MAX \
-       SFC_DIV_ROUND_UP(SFC_MBUF_SEG_LEN_MAX, \
-                        SFC_EF10_TX_DMA_DESC_LEN_MAX)
-
 /**
  * Maximum number of descriptors/buffers in the Tx ring.
  * It should guarantee that corresponding event queue never overfill.
@@ -221,6 +212,53 @@ sfc_ef10_tx_qpush(struct sfc_ef10_txq *txq, unsigned int added,
        *(volatile __m128i *)txq->doorbell = oword.eo_u128[0];
 }
 
+static unsigned int
+sfc_ef10_tx_pkt_descs_max(const struct rte_mbuf *m)
+{
+       unsigned int extra_descs_per_seg;
+       unsigned int extra_descs_per_pkt;
+
+       /*
+        * VLAN offload is not supported yet, so no extra descriptors
+        * are required for VLAN option descriptor.
+        */
+
+/** Maximum length of the mbuf segment data */
+#define SFC_MBUF_SEG_LEN_MAX           UINT16_MAX
+       RTE_BUILD_BUG_ON(sizeof(m->data_len) != 2);
+
+       /*
+        * Each segment is already counted once below.  So, calculate
+        * how many extra DMA descriptors may be required per segment in
+        * the worst case because of maximum DMA descriptor length limit.
+        * If maximum segment length is less or equal to maximum DMA
+        * descriptor length, no extra DMA descriptors are required.
+        */
+       extra_descs_per_seg =
+               (SFC_MBUF_SEG_LEN_MAX - 1) / SFC_EF10_TX_DMA_DESC_LEN_MAX;
+
+/** Maximum length of the packet */
+#define SFC_MBUF_PKT_LEN_MAX           UINT32_MAX
+       RTE_BUILD_BUG_ON(sizeof(m->pkt_len) != 4);
+
+       /*
+        * One more limitation on maximum number of extra DMA descriptors
+        * comes from slicing entire packet because of DMA descriptor length
+        * limit taking into account that there is at least one segment
+        * which is already counted below (so division of the maximum
+        * packet length minus one with round down).
+        * TSO is not supported yet, so packet length is limited by
+        * maximum PDU size.
+        */
+       extra_descs_per_pkt =
+               (RTE_MIN((unsigned int)EFX_MAC_PDU_MAX,
+                        SFC_MBUF_PKT_LEN_MAX) - 1) /
+               SFC_EF10_TX_DMA_DESC_LEN_MAX;
+
+       return m->nb_segs + RTE_MIN(m->nb_segs * extra_descs_per_seg,
+                                   extra_descs_per_pkt);
+}
+
 static uint16_t
 sfc_ef10_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 {
@@ -258,8 +296,7 @@ sfc_ef10_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
                if (likely(pktp + 1 != pktp_end))
                        rte_mbuf_prefetch_part1(pktp[1]);
 
-               if (m_seg->nb_segs * SFC_EF10_TX_MBUF_SEG_DESCS_MAX >
-                   dma_desc_space) {
+               if (sfc_ef10_tx_pkt_descs_max(m_seg) > dma_desc_space) {
                        if (reap_done)
                                break;
 
@@ -273,8 +310,7 @@ sfc_ef10_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
                        reap_done = true;
                        dma_desc_space = SFC_EF10_TXQ_LIMIT(ptr_mask + 1) -
                                (added - txq->completed);
-                       if (m_seg->nb_segs * SFC_EF10_TX_MBUF_SEG_DESCS_MAX >
-                           dma_desc_space)
+                       if (sfc_ef10_tx_pkt_descs_max(m_seg) > dma_desc_space)
                                break;
                }