net/sfc: add Rx descriptor wait timeout

Add device argument to customize Rx descriptor wait timeout which
is supported in DPDK firmware variant only in equal stride super-buffer
Rx mode only.

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Ivan Malov <ivan.malov@oktetlabs.ru>

doc/guides/nics/sfc_efx.rst

@@ -372,6 +372,18 @@ boolean parameters value.
   without checksumming on transmit for higher Tx packet rate if
   checksumming is not required.
 
+- ``rxd_wait_timeout_ns`` [long] (default **200 us**)
+
+  Adjust timeout in nanoseconds to head-of-line block to wait for
+  Rx descriptors.
+  The accepted range is 0 to 400 ms.
+  Flow control should be enabled to make it work.
+  The value of **0** disables it and packets are dropped immediately.
+  When a packet is dropped because of no Rx descriptors,
+  ``rx_nodesc_drop_cnt`` counter grows.
+  The feature is supported only by the DPDK firmware variant when equal
+  stride super-buffer Rx mode is used.
+
 
 Dynamic Logging Parameters
 ~~~~~~~~~~~~~~~~~~~~~~~~~~

drivers/net/sfc/sfc.c

@@ -21,6 +21,7 @@
 #include "sfc_rx.h"
 #include "sfc_tx.h"
 #include "sfc_kvargs.h"
+#include "sfc_tweak.h"
 
 
 int
@@ -899,6 +900,32 @@ sfc_fw_variant2str(efx_fw_variant_t efv)
 	}
 }
 
+static int
+sfc_kvarg_rxd_wait_timeout_ns(struct sfc_adapter *sa)
+{
+	int rc;
+	long value;
+
+	value = SFC_RXD_WAIT_TIMEOUT_NS_DEF;
+
+	rc = sfc_kvargs_process(sa, SFC_KVARG_RXD_WAIT_TIMEOUT_NS,
+				sfc_kvarg_long_handler, &value);
+	if (rc != 0)
+		return rc;
+
+	if (value < 0 ||
+	    (unsigned long)value > EFX_RXQ_ES_SUPER_BUFFER_HOL_BLOCK_MAX) {
+		sfc_err(sa, "wrong '" SFC_KVARG_RXD_WAIT_TIMEOUT_NS "' "
+			    "was set (%ld);", value);
+		sfc_err(sa, "it must not be less than 0 or greater than %u",
+			    EFX_RXQ_ES_SUPER_BUFFER_HOL_BLOCK_MAX);
+		return EINVAL;
+	}
+
+	sa->rxd_wait_timeout_ns = value;
+	return 0;
+}
+
 static int
 sfc_nic_probe(struct sfc_adapter *sa)
 {
@@ -916,6 +943,10 @@ sfc_nic_probe(struct sfc_adapter *sa)
 		return rc;
 	}
 
+	rc = sfc_kvarg_rxd_wait_timeout_ns(sa);
+	if (rc != 0)
+		return rc;
+
 	rc = efx_nic_probe(enp, preferred_efv);
 	if (rc == EACCES) {
 		/* Unprivileged functions cannot set FW variant */

drivers/net/sfc/sfc.h

@@ -238,6 +238,8 @@ struct sfc_adapter {
 
 	boolean_t			tso;
 
+	uint32_t			rxd_wait_timeout_ns;
+
 	struct sfc_rss			rss;
 
 	/*

drivers/net/sfc/sfc_ethdev.c

@@ -2109,6 +2109,7 @@ RTE_PMD_REGISTER_PARAM_STRING(net_sfc_efx,
 	SFC_KVARG_TX_DATAPATH "=" SFC_KVARG_VALUES_TX_DATAPATH " "
 	SFC_KVARG_PERF_PROFILE "=" SFC_KVARG_VALUES_PERF_PROFILE " "
 	SFC_KVARG_FW_VARIANT "=" SFC_KVARG_VALUES_FW_VARIANT " "
+	SFC_KVARG_RXD_WAIT_TIMEOUT_NS "=<long> "
 	SFC_KVARG_STATS_UPDATE_PERIOD_MS "=<long>");
 
 RTE_INIT(sfc_driver_register_logtype);

drivers/net/sfc/sfc_kvargs.c

@@ -27,6 +27,7 @@ sfc_kvargs_parse(struct sfc_adapter *sa)
 		SFC_KVARG_RX_DATAPATH,
 		SFC_KVARG_TX_DATAPATH,
 		SFC_KVARG_FW_VARIANT,
+		SFC_KVARG_RXD_WAIT_TIMEOUT_NS,
 		NULL,
 	};
 

drivers/net/sfc/sfc_kvargs.h

@@ -61,6 +61,8 @@ extern "C" {
 	    SFC_KVARG_FW_VARIANT_PACKED_STREAM "|" \
 	    SFC_KVARG_FW_VARIANT_DPDK "]"
 
+#define SFC_KVARG_RXD_WAIT_TIMEOUT_NS	"rxd_wait_timeout_ns"
+
 struct sfc_adapter;
 
 int sfc_kvargs_parse(struct sfc_adapter *sa);

drivers/net/sfc/sfc_rx.c

@@ -703,7 +703,7 @@ sfc_rx_qstart(struct sfc_adapter *sa, unsigned int sw_index)
 		rc = efx_rx_qcreate_es_super_buffer(sa->nic, rxq->hw_index, 0,
 			mp_info.contig_block_size, rxq->buf_size,
 			mp->header_size + mp->elt_size + mp->trailer_size,
-			0 /* hol_block_timeout */,
+			sa->rxd_wait_timeout_ns,
 			&rxq->mem, rxq_info->entries, rxq_info->type_flags,
 			evq->common, &rxq->common);
 		break;

drivers/net/sfc/sfc_tweak.h

@@ -34,4 +34,12 @@
 /** Number of mbufs to be freed in bulk in a single call */
 #define SFC_TX_REAP_BULK_SIZE		32
 
+/**
+ * Default head-of-line block timeout to wait for Rx descriptor before
+ * packet drop because of no descriptors available.
+ *
+ * DPDK FW variant only with equal stride super-buffer Rx mode.
+ */
+#define SFC_RXD_WAIT_TIMEOUT_NS_DEF	(200U * 1000)
+
 #endif /* _SFC_TWEAK_H_ */