net/netvsc: allow tuning latency with devargs

Allow overriding default guest to host latency on per device basis
with devargs.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>

diff --git a/doc/guides/nics/netvsc.rst b/doc/guides/nics/netvsc.rst
index 345f393..cc07ce4 100644 (file)
--- a/doc/guides/nics/netvsc.rst
+++ b/doc/guides/nics/netvsc.rst
@@ -103,3 +103,19 @@ The following prerequisites apply:
 *   Linux kernel support for UIO on vmbus is done with the uio_hv_generic driver.
     Full support of multiple queues requires the 4.17 kernel. It is possible
     to use the netvsc PMD with 4.16 kernel but it is limited to a single queue.
+
+
+Netvsc PMD arguments
+--------------------
+
+The user can specify below argument in devargs.
+
+#.  ``latency``:
+
+    A netvsc device uses a mailbox page to indicate to the host that there
+    is something in the transmit queue. The host scans this page at a
+    periodic interval. This parameter allows adjusting the value that
+    is used by the host. Smaller values improve transmit latency, and larger
+    values save CPU cycles. This parameter is in microseconds.
+    If the value is too large or too small it will be
+    ignored by the host. (Default: 50)

diff --git a/drivers/net/netvsc/hn_ethdev.c b/drivers/net/netvsc/hn_ethdev.c
index 7f7ac15..e61ff43 100644 (file)
--- a/drivers/net/netvsc/hn_ethdev.c
+++ b/drivers/net/netvsc/hn_ethdev.c
@@ -14,7 +14,9 @@
 #include <rte_memcpy.h>
 #include <rte_string_fns.h>
 #include <rte_memzone.h>
+#include <rte_devargs.h>
 #include <rte_malloc.h>
+#include <rte_kvargs.h>
 #include <rte_atomic.h>
 #include <rte_branch_prediction.h>
 #include <rte_ether.h>
@@ -130,6 +132,55 @@ eth_dev_vmbus_release(struct rte_eth_dev *eth_dev)
        eth_dev->intr_handle = NULL;
 }
 
+/* handle "latency=X" from devargs */
+static int hn_set_latency(const char *key, const char *value, void *opaque)
+{
+       struct hn_data *hv = opaque;
+       char *endp = NULL;
+       unsigned long lat;
+
+       errno = 0;
+       lat = strtoul(value, &endp, 0);
+
+       if (*value == '\0' || *endp != '\0') {
+               PMD_DRV_LOG(ERR, "invalid parameter %s=%s", key, value);
+               return -EINVAL;
+       }
+
+       PMD_DRV_LOG(DEBUG, "set latency %lu usec", lat);
+
+       hv->latency = lat * 1000;       /* usec to nsec */
+       return 0;
+}
+
+/* Parse device arguments */
+static int hn_parse_args(const struct rte_eth_dev *dev)
+{
+       struct hn_data *hv = dev->data->dev_private;
+       struct rte_devargs *devargs = dev->device->devargs;
+       static const char * const valid_keys[] = {
+               "latency",
+               NULL
+       };
+       struct rte_kvargs *kvlist;
+
+       if (!devargs)
+               return 0;
+
+       PMD_INIT_LOG(DEBUG, "device args %s %s",
+                    devargs->name, devargs->args);
+
+       kvlist = rte_kvargs_parse(devargs->args, valid_keys);
+       if (!kvlist) {
+               PMD_DRV_LOG(NOTICE, "invalid parameters");
+               return -EINVAL;
+       }
+
+       rte_kvargs_process(kvlist, "latency", hn_set_latency, hv);
+       rte_kvargs_free(kvlist);
+       return 0;
+}
+
 /* Update link status.
  * Note: the DPDK definition of "wait_to_complete"
  *   means block this call until link is up.
@@ -263,8 +314,7 @@ static int hn_subchan_configure(struct hn_data *hv,
                        return err;
                }
 
-               rte_vmbus_set_latency(hv->vmbus, new_sc,
-                                     HN_CHAN_LATENCY_NS);
+               rte_vmbus_set_latency(hv->vmbus, new_sc, hv->latency);
 
                retry = 0;
                chn_index = rte_vmbus_sub_channel_index(new_sc);
@@ -626,14 +676,18 @@ eth_hn_dev_init(struct rte_eth_dev *eth_dev)
        hv->rxbuf_res = &vmbus->resource[HV_RECV_BUF_MAP];
        hv->chim_res  = &vmbus->resource[HV_SEND_BUF_MAP];
        hv->port_id = eth_dev->data->port_id;
+       hv->latency = HN_CHAN_LATENCY_NS;
+
+       err = hn_parse_args(eth_dev);
+       if (err)
+               return err;
 
        /* Initialize primary channel input for control operations */
        err = rte_vmbus_chan_open(vmbus, &hv->channels[0]);
        if (err)
                return err;
 
-       rte_vmbus_set_latency(hv->vmbus, hv->channels[0],
-                             HN_CHAN_LATENCY_NS);
+       rte_vmbus_set_latency(hv->vmbus, hv->channels[0], hv->latency);
 
        hv->primary = hn_rx_queue_alloc(hv, 0,
                                        eth_dev->device->numa_node);

diff --git a/drivers/net/netvsc/hn_var.h b/drivers/net/netvsc/hn_var.h
index b42bd97..f188f63 100644 (file)
--- a/drivers/net/netvsc/hn_var.h
+++ b/drivers/net/netvsc/hn_var.h
@@ -113,6 +113,7 @@ struct hn_data {
        uint32_t        chim_szmax;             /* Max size per buffer */
        uint32_t        chim_cnt;               /* Max packets per buffer */
 
+       uint32_t        latency;
        uint32_t        nvs_ver;
        uint32_t        ndis_ver;
        uint32_t        rndis_agg_size;