net/netvsc: control use of external mbuf on Rx

When receiving packets, netvsp puts data in a buffer mapped through UIO.
Depending on packet size, netvsc may attach the buffer as an external
mbuf. This is not a problem if this mbuf is consumed in the application,
and the application can correctly read data out of an external mbuf.

However, there are two problems with data in an external mbuf.
1. Due to the limitation of the kernel UIO implementation, physical
   address of this external buffer is not exposed to the user-mode. If
   this mbuf is passed to another driver, the other driver is unable to
   map this buffer to iova.
2. Some DPDK applications are not aware of external mbuf, and may bug
   when they receive an mbuf with external buffer attached.

Introduce a driver parameter "rx_extmbuf_enable" to control if netvsc
should use external mbuf for receiving packets. The default value is 0.
(netvsc doesn't use external mbuf, it always allocates mbuf and copy
data to mbuf) A non-zero value tells netvsc to attach external buffers
to mbuf on receiving packets, thus avoid copying memory.

Signed-off-by: Long Li <longli@microsoft.com>

diff --git a/doc/guides/nics/netvsc.rst b/doc/guides/nics/netvsc.rst
index 5a68ffa..19f9940 100644 (file)
--- a/doc/guides/nics/netvsc.rst
+++ b/doc/guides/nics/netvsc.rst
@@ -133,3 +133,11 @@ The user can specify below argument in devargs.
     set larger than the MTU, then all packets smaller than the chunk size
     of the VMBus send buffer will be copied; larger packets always have to
     go as a single direct request. The default value is 512 (bytes).
+
+#.  ``rx_extmbuf_enable``:
+    The rx_extmbuf_enable is used to control if netvsc should use external
+    mbuf for receiving packets. The default value is 0. (netvsc doesn't use
+    external mbuf, it always allocates mbuf and copy received data to mbuf)
+    A non-zero value tells netvsc to attach external buffers to mbuf on
+    receiving packets, thus avoid copying memory. Use of external buffers
+    requires the application is able to read data from external mbuf.

diff --git a/drivers/net/netvsc/hn_ethdev.c b/drivers/net/netvsc/hn_ethdev.c
index f7a02ef..49f9543 100644 (file)
--- a/drivers/net/netvsc/hn_ethdev.c
+++ b/drivers/net/netvsc/hn_ethdev.c
@@ -48,6 +48,7 @@
 #define NETVSC_ARG_LATENCY "latency"
 #define NETVSC_ARG_RXBREAK "rx_copybreak"
 #define NETVSC_ARG_TXBREAK "tx_copybreak"
+#define NETVSC_ARG_RX_EXTMBUF_ENABLE "rx_extmbuf_enable"
 
 struct hn_xstats_name_off {
        char name[RTE_ETH_XSTATS_NAME_SIZE];
@@ -164,6 +165,10 @@ static int hn_set_parameter(const char *key, const char *value, void *opaque)
                hv->tx_copybreak = v;
                PMD_DRV_LOG(DEBUG, "tx copy break set to %u",
                            hv->tx_copybreak);
+       } else if (!strcmp(key, NETVSC_ARG_RX_EXTMBUF_ENABLE)) {
+               hv->rx_extmbuf_enable = v;
+               PMD_DRV_LOG(DEBUG, "rx extmbuf enable set to %u",
+                           hv->rx_extmbuf_enable);
        }
 
        return 0;
@@ -178,6 +183,7 @@ static int hn_parse_args(const struct rte_eth_dev *dev)
                NETVSC_ARG_LATENCY,
                NETVSC_ARG_RXBREAK,
                NETVSC_ARG_TXBREAK,
+               NETVSC_ARG_RX_EXTMBUF_ENABLE,
                NULL
        };
        struct rte_kvargs *kvlist;
@@ -980,6 +986,7 @@ eth_hn_dev_init(struct rte_eth_dev *eth_dev)
        hv->latency = HN_CHAN_LATENCY_NS;
        hv->rx_copybreak = HN_RXCOPY_THRESHOLD;
        hv->tx_copybreak = HN_TXCOPY_THRESHOLD;
+       hv->rx_extmbuf_enable = HN_RX_EXTMBUF_ENABLE;
        hv->max_queues = 1;
 
        rte_rwlock_init(&hv->vf_lock);
@@ -1140,4 +1147,5 @@ RTE_LOG_REGISTER(hn_logtype_driver, pmd.net.netvsc.driver, NOTICE);
 RTE_PMD_REGISTER_PARAM_STRING(net_netvsc,
                              NETVSC_ARG_LATENCY "=<uint32> "
                              NETVSC_ARG_RXBREAK "=<uint32> "
-                             NETVSC_ARG_TXBREAK "=<uint32>");
+                             NETVSC_ARG_TXBREAK "=<uint32> "
+                             NETVSC_ARG_RX_EXTMBUF_ENABLE "=<0|1>");

diff --git a/drivers/net/netvsc/hn_rxtx.c b/drivers/net/netvsc/hn_rxtx.c
index 674520c..015662f 100644 (file)
--- a/drivers/net/netvsc/hn_rxtx.c
+++ b/drivers/net/netvsc/hn_rxtx.c
@@ -570,7 +570,7 @@ static void hn_rxpkt(struct hn_rx_queue *rxq, struct hn_rx_bufinfo *rxb,
         * For large packets, avoid copy if possible but need to keep
         * some space available in receive area for later packets.
         */
-       if (dlen > hv->rx_copybreak &&
+       if (hv->rx_extmbuf_enable && dlen > hv->rx_copybreak &&
            (uint32_t)rte_atomic32_read(&rxq->rxbuf_outstanding) <
                        hv->rxbuf_section_cnt / 2) {
                struct rte_mbuf_ext_shared_info *shinfo;

diff --git a/drivers/net/netvsc/hn_var.h b/drivers/net/netvsc/hn_var.h
index 774e6bb..bd874c6 100644 (file)
--- a/drivers/net/netvsc/hn_var.h
+++ b/drivers/net/netvsc/hn_var.h
@@ -26,6 +26,8 @@
 #define HN_TXCOPY_THRESHOLD    512
 #define HN_RXCOPY_THRESHOLD    256
 
+#define HN_RX_EXTMBUF_ENABLE   0
+
 /* Buffers need to be aligned */
 #ifndef PAGE_SIZE
 #define PAGE_SIZE 4096
@@ -120,6 +122,7 @@ struct hn_data {
        struct rte_mem_resource *rxbuf_res;     /* UIO resource for Rx */
        uint32_t        rxbuf_section_cnt;      /* # of Rx sections */
        uint32_t        rx_copybreak;
+       uint32_t        rx_extmbuf_enable;
        uint16_t        max_queues;             /* Max available queues */
        uint16_t        num_queues;
        uint64_t        rss_offloads;