dpif-netdev: Add parameters to configure PMD auto load balance.

Two important parts of how PMD auto load balance operates are how
loaded a core needs to be and how much improvement is estimated
before a PMD auto load balance can trigger.

Previously they were hardcoded to 95% loaded and 25% variance
improvement.

These default values may not be suitable for all use cases and
we may want to use a more (or less) aggressive rebalance, either
on the pmd load threshold or on the minimum variance improvement
threshold.

The defaults are not changed, but "pmd-auto-lb-load-threshold" and
"pmd-auto-lb-improvement-threshold" parameters are added to override
the defaults.

$ ovs-vsctl set open_vswitch . other_config:pmd-auto-lb-load-threshold="70"
$ ovs-vsctl set open_vswitch . other_config:pmd-auto-lb-improvement-threshold="20"

Signed-off-by: Christophe Fontaine <cfontain@redhat.com>
Co-Authored-by: Kevin Traynor <ktraynor@redhat.com>
Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
Acked-by: David Marchand <david.marchand@redhat.com>
Acked-by: Ian Stokes <ian.stokes@intel.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

NEWS

@@ -20,6 +20,9 @@ Post-v2.14.0
      * Add generic IP protocol support to conntrack. With this change, all
        none UDP, TCP, and ICMP traffic will be treated as general L3
        traffic, i.e. using 3 tupples.
+     * Add parameters 'pmd-auto-lb-load-threshold' and
+       'pmd-auto-lb-improvement-threshold' to configure PMD auto load balance
+       behaviour.
    - The environment variable OVS_UNBOUND_CONF, if set, is now used
      as the DNS resolver's (unbound) configuration file.
    - Linux datapath:

lib/dpif-netdev.c

@@ -85,9 +85,9 @@
 VLOG_DEFINE_THIS_MODULE(dpif_netdev);
 
 /* Auto Load Balancing Defaults */
-#define ALB_ACCEPTABLE_IMPROVEMENT       25
+#define ALB_IMPROVEMENT_THRESHOLD    25
-#define ALB_PMD_LOAD_THRESHOLD           95
+#define ALB_LOAD_THRESHOLD           95
-#define ALB_PMD_REBALANCE_POLL_INTERVAL  1 /* 1 Min */
+#define ALB_REBALANCE_INTERVAL       1 /* 1 Min */
 #define MIN_TO_MSEC                  60000
 
 #define FLOW_DUMP_MAX_BATCH 50
@@ -300,6 +300,8 @@ struct pmd_auto_lb {
     bool is_enabled;            /* Current status of Auto load balancing. */
     uint64_t rebalance_intvl;
     uint64_t rebalance_poll_timer;
+    uint8_t rebalance_improve_thresh;
+    atomic_uint8_t rebalance_load_thresh;
 };
 
 /* Datapath based on the network device interface from netdev.h.
@@ -4204,6 +4206,7 @@ set_pmd_auto_lb(struct dp_netdev *dp)
     unsigned int cnt = 0;
     struct dp_netdev_pmd_thread *pmd;
     struct pmd_auto_lb *pmd_alb = &dp->pmd_alb;
+    uint8_t rebalance_load_thresh;
 
     bool enable_alb = false;
     bool multi_rxq = false;
@@ -4233,9 +4236,16 @@ set_pmd_auto_lb(struct dp_netdev *dp)
     if (pmd_alb->is_enabled != enable_alb) {
         pmd_alb->is_enabled = enable_alb;
         if (pmd_alb->is_enabled) {
+            atomic_read_relaxed(&pmd_alb->rebalance_load_thresh,
+                                &rebalance_load_thresh);
             VLOG_INFO("PMD auto load balance is enabled "
-                      "interval %"PRIu64" mins",
+                      "interval %"PRIu64" mins, "
-                       pmd_alb->rebalance_intvl / MIN_TO_MSEC);
+                      "pmd load threshold %"PRIu8"%%, "
+                      "improvement threshold %"PRIu8"%%",
+                       pmd_alb->rebalance_intvl / MIN_TO_MSEC,
+                       rebalance_load_thresh,
+                       pmd_alb->rebalance_improve_thresh);
+
         } else {
             pmd_alb->rebalance_poll_timer = 0;
             VLOG_INFO("PMD auto load balance is disabled");
@@ -4259,6 +4269,8 @@ dpif_netdev_set_config(struct dpif *dpif, const struct smap *other_config)
     uint32_t insert_min, cur_min;
     uint32_t tx_flush_interval, cur_tx_flush_interval;
     uint64_t rebalance_intvl;
+    uint8_t rebalance_load, cur_rebalance_load;
+    uint8_t rebalance_improve;
 
     tx_flush_interval = smap_get_int(other_config, "tx-flush-interval",
                                      DEFAULT_TX_FLUSH_INTERVAL);
@@ -4336,7 +4348,7 @@ dpif_netdev_set_config(struct dpif *dpif, const struct smap *other_config)
                               false);
 
     rebalance_intvl = smap_get_int(other_config, "pmd-auto-lb-rebal-interval",
-                              ALB_PMD_REBALANCE_POLL_INTERVAL);
+                                   ALB_REBALANCE_INTERVAL);
 
     /* Input is in min, convert it to msec. */
     rebalance_intvl =
@@ -4348,6 +4360,30 @@ dpif_netdev_set_config(struct dpif *dpif, const struct smap *other_config)
                   "%"PRIu64" mins\n", rebalance_intvl / MIN_TO_MSEC);
     }
 
+    rebalance_improve = smap_get_int(other_config,
+                                     "pmd-auto-lb-improvement-threshold",
+                                     ALB_IMPROVEMENT_THRESHOLD);
+    if (rebalance_improve > 100) {
+        rebalance_improve = ALB_IMPROVEMENT_THRESHOLD;
+    }
+    if (rebalance_improve != pmd_alb->rebalance_improve_thresh) {
+        pmd_alb->rebalance_improve_thresh = rebalance_improve;
+        VLOG_INFO("PMD auto load balance improvement threshold set to "
+                  "%"PRIu8"%%", rebalance_improve);
+    }
+
+    rebalance_load = smap_get_int(other_config, "pmd-auto-lb-load-threshold",
+                                  ALB_LOAD_THRESHOLD);
+    if (rebalance_load > 100) {
+        rebalance_load = ALB_LOAD_THRESHOLD;
+    }
+    atomic_read_relaxed(&pmd_alb->rebalance_load_thresh, &cur_rebalance_load);
+    if (rebalance_load != cur_rebalance_load) {
+        atomic_store_relaxed(&pmd_alb->rebalance_load_thresh,
+                             rebalance_load);
+        VLOG_INFO("PMD auto load balance load threshold set to %"PRIu8"%%",
+                  rebalance_load);
+    }
     set_pmd_auto_lb(dp);
     return 0;
 }
@@ -5676,7 +5712,7 @@ pmd_rebalance_dry_run(struct dp_netdev *dp)
             improvement =
                 ((curr_variance - new_variance) * 100) / curr_variance;
         }
-        if (improvement < ALB_ACCEPTABLE_IMPROVEMENT) {
+        if (improvement < dp->pmd_alb.rebalance_improve_thresh) {
             ret = false;
         }
     }
@@ -8711,6 +8747,7 @@ dp_netdev_pmd_try_optimize(struct dp_netdev_pmd_thread *pmd,
 
     if (pmd->ctx.now > pmd->rxq_next_cycle_store) {
         uint64_t curr_tsc;
+        uint8_t rebalance_load_trigger;
         struct pmd_auto_lb *pmd_alb = &pmd->dp->pmd_alb;
         if (pmd_alb->is_enabled && !pmd->isolated
             && (pmd->perf_stats.counters.n[PMD_CYCLES_ITER_IDLE] >=
@@ -8727,7 +8764,9 @@ dp_netdev_pmd_try_optimize(struct dp_netdev_pmd_thread *pmd,
                 pmd_load = ((tot_proc * 100) / (tot_idle + tot_proc));
             }
 
-            if (pmd_load >= ALB_PMD_LOAD_THRESHOLD) {
+            atomic_read_relaxed(&pmd_alb->rebalance_load_thresh,
+                                &rebalance_load_trigger);
+            if (pmd_load >= rebalance_load_trigger) {
                 atomic_count_inc(&pmd->pmd_overloaded);
             } else {
                 atomic_count_set(&pmd->pmd_overloaded, 0);

vswitchd/vswitch.xml

@@ -653,8 +653,9 @@
               type='{"type": "boolean"}'>
         <p>
          Configures PMD Auto Load Balancing that allows automatic assignment of
-         RX queues to PMDs if any of PMDs is overloaded (i.e. processing cycles
+         RX queues to PMDs if any of PMDs is overloaded (i.e. a processing
-         > 95%).
+         cycles >
+         <ref column="other_config" key="pmd-auto-lb-load-threshold"/>).
         </p>
         <p>
          It uses current scheme of cycle based assignment of RX queues that
@@ -690,6 +691,32 @@
          once in few hours or a day or a week.
         </p>
       </column>
+      <column name="other_config" key="pmd-auto-lb-load-threshold"
+              type='{"type": "integer", "minInteger": 0, "maxInteger": 100}'>
+        <p>
+         Specifies the minimum PMD thread load threshold (% of used cycles) of
+         any non-isolated PMD threads when a PMD Auto Load Balance may be
+         triggered.
+        </p>
+        <p>
+         The default value is <code>95%</code>.
+        </p>
+      </column>
+      <column name="other_config" key="pmd-auto-lb-improvement-threshold"
+              type='{"type": "integer", "minInteger": 0, "maxInteger": 100}'>
+        <p>
+         Specifies the minimum evaluated % improvement in load distribution
+         across the non-isolated PMD threads that will allow a PMD Auto Load
+         Balance to occur.
+        </p>
+        <p>
+         Note, setting this parameter to 0 will always allow an auto load
+         balance to occur regardless of estimated improvement or not.
+        </p>
+        <p>
+         The default value is <code>25%</code>.
+        </p>
+      </column>
       <column name="other_config" key="userspace-tso-enable"
               type='{"type": "boolean"}'>
         <p>