[ovs-dev] [PATCH 3/3] netdev-dpdk: Enable vhost-tx-retries config.

Kevin Traynor ktraynor at redhat.com
Fri Jun 21 13:41:58 UTC 2019


vhost tx retries can provide some mitigation against
dropped packets due to a temporarily slow guest/limited queue
size for an interface, but on the other hand when a system
is fully loaded those extra cycles retrying could mean
packets are dropped elsewhere.

Up to now max vhost retries have been hardcoded, which meant
no tuning and no way to disable for debugging to see if extra
cycles spent retrying resulted in rx drops on some other
interface.

Add an option to change the max retries, with a value of
0 effectively disabling vhost tx retries.

Signed-off-by: Kevin Traynor <ktraynor at redhat.com>
---
 Documentation/topics/dpdk/vhost-user.rst | 26 ++++++++++++++++++++++++
 lib/netdev-dpdk.c                        | 26 ++++++++++++++++++++----
 vswitchd/vswitch.xml                     | 10 +++++++++
 3 files changed, 58 insertions(+), 4 deletions(-)

diff --git a/Documentation/topics/dpdk/vhost-user.rst b/Documentation/topics/dpdk/vhost-user.rst
index e79ed082e..0b14bc999 100644
--- a/Documentation/topics/dpdk/vhost-user.rst
+++ b/Documentation/topics/dpdk/vhost-user.rst
@@ -387,4 +387,30 @@ The default value is ``false``.
 .. _dpdk-testpmd:
 
+vhost-user-client tx retries
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+For vhost-user-client interfaces, the max amount of retries can be changed from
+the default 8 by setting ``vhost-tx-retries``.
+
+The minimum is 0 which means there will be no retries and if any packets in
+each batch cannot be sent immediately they will be dropped. The maximum is 31,
+which would mean that after the first packet(s) in the batch was sent there
+could be up to a separate retry for each of the remaining packets, until they
+are all sent or no packet was sent during a retry.
+
+Retries can help with avoiding packet loss when temporarily unable to a vhost
+interface because the virtqueue is full. However, spending more time retrying
+to send to one interface, will reduce the time available for rx/tx and
+processing packets on other interfaces, so some tuning may be required for best
+performance.
+
+Tx retries can be set for vhost-user-client ports::
+
+    $ ovs-vsctl set Interface vhost-client-1 options:vhost-tx-retries=0
+
+.. note::
+
+ Configurable vhost tx retries are not supported with vhost-user ports.
+
 DPDK in the Guest
 -----------------
diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
index 03a8de380..8ae1093d8 100644
--- a/lib/netdev-dpdk.c
+++ b/lib/netdev-dpdk.c
@@ -409,5 +409,6 @@ struct netdev_dpdk {
         /* True if vHost device is 'up' and has been reconfigured at least once */
         bool vhost_reconfigured;
-        /* 3 pad bytes here. */
+        atomic_uint8_t vhost_tx_retries;
+        /* 2 pad bytes here. */
     );
 
@@ -1240,4 +1241,6 @@ vhost_common_construct(struct netdev *netdev)
     }
 
+    atomic_store_relaxed(&dev->vhost_tx_retries, VHOST_ENQ_RETRY_NUM);
+
     return common_construct(netdev, DPDK_ETH_PORT_ID_INVALID,
                             DPDK_DEV_VHOST, socket_id);
@@ -1899,4 +1902,5 @@ netdev_dpdk_vhost_client_set_config(struct netdev *netdev,
     struct netdev_dpdk *dev = netdev_dpdk_cast(netdev);
     const char *path;
+    int max_tx_retries, cur_max_tx_retries;
 
     ovs_mutex_lock(&dev->mutex);
@@ -1915,4 +1919,13 @@ netdev_dpdk_vhost_client_set_config(struct netdev *netdev,
         }
     }
+
+    max_tx_retries = smap_get_int(args, "vhost-tx-retries",
+                                  VHOST_ENQ_RETRY_NUM);
+    atomic_read_relaxed(&dev->vhost_tx_retries, &cur_max_tx_retries);
+    if (max_tx_retries != cur_max_tx_retries) {
+        atomic_store_relaxed(&dev->vhost_tx_retries, max_tx_retries);
+        VLOG_INFO("Max Tx retries for vhost device '%s' set to %d",
+                  dev->up.name, max_tx_retries);
+    }
     ovs_mutex_unlock(&dev->mutex);
 
@@ -2299,4 +2312,5 @@ netdev_dpdk_vhost_update_tx_counters(struct netdev_stats *stats,
                                      int attempted,
                                      int dropped,
+                                     int max_retries,
                                      int retries)
 {
@@ -2306,5 +2320,5 @@ netdev_dpdk_vhost_update_tx_counters(struct netdev_stats *stats,
     stats->tx_packets += sent;
     stats->tx_dropped += dropped;
-    stats->tx_retries += MIN(retries, VHOST_ENQ_RETRY_NUM);
+    stats->tx_retries += MIN(retries, max_retries);
 
     for (i = 0; i < sent; i++) {
@@ -2323,4 +2337,5 @@ __netdev_dpdk_vhost_send(struct netdev *netdev, int qid,
     int i, retries = 0;
     int vid = netdev_dpdk_get_vid(dev);
+    int max_retries = 0;
 
     qid = dev->tx_q[qid % netdev->n_txq].map;
@@ -2351,9 +2366,12 @@ __netdev_dpdk_vhost_send(struct netdev *netdev, int qid,
             /* Prepare for possible retry.*/
             cur_pkts = &cur_pkts[tx_pkts];
+            if (OVS_UNLIKELY(cnt && !retries)) {
+                atomic_read_relaxed(&dev->vhost_tx_retries, &max_retries);
+            }
         } else {
             /* No packets sent - do not retry.*/
             break;
         }
-    } while (cnt && (retries++ < VHOST_ENQ_RETRY_NUM));
+    } while (cnt && (retries++ < max_retries));
 
     rte_spinlock_unlock(&dev->tx_q[qid].tx_lock);
@@ -2361,5 +2379,5 @@ __netdev_dpdk_vhost_send(struct netdev *netdev, int qid,
     rte_spinlock_lock(&dev->stats_lock);
     netdev_dpdk_vhost_update_tx_counters(&dev->stats, pkts, total_pkts,
-                                         cnt + dropped, retries);
+                                         cnt + dropped, max_retries, retries);
     rte_spinlock_unlock(&dev->stats_lock);
 
diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
index bf4b6f8dc..7ffbdd77a 100644
--- a/vswitchd/vswitch.xml
+++ b/vswitchd/vswitch.xml
@@ -3127,4 +3127,14 @@ ovs-vsctl add-port br0 p0 -- set Interface p0 type=patch options:peer=p1 \
       </column>
 
+      <column name="options" key="vhost-tx-retries"
+              type='{"type": "integer", "minInteger": 0, "maxInteger": 31}'>
+        <p>
+          The value specifies the maximum amount of tx vhost retries that can
+          be made while trying to send a batch of packets to a dpdkvhostclient
+          interface. The max batch size is 32 packets.
+          Only supported by dpdkvhostuserclient interfaces.
+        </p>
+      </column>
+
       <column name="options" key="n_rxq_desc"
               type='{"type": "integer", "minInteger": 1, "maxInteger": 4096}'>
-- 
2.20.1



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