dpif-netdev: Add round-robin based rxq to pmd assignment.

Prior to OVS 2.9 automatic assignment of Rxqs to PMDs
(i.e. CPUs) was done by round-robin.

That was changed in OVS 2.9 to ordering the Rxqs based on
their measured processing cycles. This was to assign the
busiest Rxqs to different PMDs, improving aggregate
throughput.

For the most part the new scheme should be better, but
there could be situations where a user prefers a simple
round-robin scheme because Rxqs from a single port are
more likely to be spread across multiple PMDs, and/or
traffic is very bursty/unpredictable.

Add 'pmd-rxq-assign' config to allow a user to select
round-robin based assignment.

Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
Acked-by: Eelco Chaudron <echaudro@redhat.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

5 files changed, 126 insertions, 30 deletions

diff --git a/Documentation/topics/dpdk/pmd.rst b/Documentation/topics/dpdk/pmd.rst
index 5f0671ecc..dd9172d65 100644
--- a/Documentation/topics/dpdk/pmd.rst
+++ b/Documentation/topics/dpdk/pmd.rst
@@ -112,12 +112,17 @@ means that this thread will only poll the *pinned* Rx queues.
    by any PMD thread.
 
 If ``pmd-rxq-affinity`` is not set for Rx queues, they will be assigned to PMDs
-(cores) automatically. Where known, the processing cycles that have been stored
-for each Rx queue will be used to assign Rx queue to PMDs based on a round
-robin of the sorted Rx queues. For example, take the following example, where
-there are five Rx queues and three cores - 3, 7, and 8 - available and the
-measured usage of core cycles per Rx queue over the last interval is seen to
-be:
+(cores) automatically.
+
+The algorithm used to automatically assign Rxqs to PMDs can be set by::
+
+    $ ovs-vsctl set Open_vSwitch . other_config:pmd-rxq-assign=<assignment>
+
+By default, ``cycles`` assignment is used where the Rxqs will be ordered by
+their measured processing cycles, and then be evenly assigned in descending
+order to PMDs based on an up/down walk of the PMDs. For example, where there
+are five Rx queues and three cores - 3, 7, and 8 - available and the measured
+usage of core cycles per Rx queue over the last interval is seen to be:
 
 - Queue #0: 30%
 - Queue #1: 80%
@@ -131,6 +136,22 @@ The Rx queues will be assigned to the cores in the following order::
     Core 7: Q4 (70%) | Q5 (10%)
     Core 8: Q3 (60%) | Q0 (30%)
 
+Alternatively, ``roundrobin`` assignment can be used, where the Rxqs are
+assigned to PMDs in a round-robined fashion. This algorithm was used by
+default prior to OVS 2.9. For example, given the following ports and queues:
+
+- Port #0 Queue #0 (P0Q0)
+- Port #0 Queue #1 (P0Q1)
+- Port #1 Queue #0 (P1Q0)
+- Port #1 Queue #1 (P1Q1)
+- Port #1 Queue #2 (P1Q2)
+
+The Rx queues may be assigned to the cores in the following order::
+
+    Core 3: P0Q0 | P1Q1
+    Core 7: P0Q1 | P1Q2
+    Core 8: P1Q0 |
+
 To see the current measured usage history of PMD core cycles for each Rx
 queue::
 
diff --git a/NEWS b/NEWS
index 33b4d8a23..33b36382c 100644
--- a/NEWS
+++ b/NEWS
@@ -8,7 +8,9 @@ Post-v2.10.0
      as the default timeout for control utilities.
    - ovn:
      * ovn-ctl: allow passing user:group ids to the OVN daemons.
-
+   - DPDK:
+     * Add option for simple round-robin based Rxq to PMD assignment.
+       It can be set with pmd-rxq-assign.
 
 v2.10.0 - xx xxx xxxx
 ---------------------
diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 9fb82ccd4..e322f5553 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -348,6 +348,8 @@ struct dp_netdev {
     /* id pool for per thread static_tx_qid. */
     struct id_pool *tx_qid_pool;
     struct ovs_mutex tx_qid_pool_mutex;
+    /* Use measured cycles for rxq to pmd assignment. */
+    bool pmd_rxq_assign_cyc;
 
     /* Protects the access of the 'struct dp_netdev_pmd_thread'
      * instance for non-pmd thread. */
@@ -1499,6 +1501,7 @@ create_dp_netdev(const char *name, const struct dpif_class *class,
     atomic_init(&dp->tx_flush_interval, DEFAULT_TX_FLUSH_INTERVAL);
 
     cmap_init(&dp->poll_threads);
+    dp->pmd_rxq_assign_cyc = true;
 
     ovs_mutex_init(&dp->tx_qid_pool_mutex);
     /* We need 1 Tx queue for each possible core + 1 for non-PMD threads. */
@@ -3726,6 +3729,8 @@ dpif_netdev_set_config(struct dpif *dpif, const struct smap *other_config)
 {
     struct dp_netdev *dp = get_dp_netdev(dpif);
     const char *cmask = smap_get(other_config, "pmd-cpu-mask");
+    const char *pmd_rxq_assign = smap_get_def(other_config, "pmd-rxq-assign",
+                                             "cycles");
     unsigned long long insert_prob =
         smap_get_ullong(other_config, "emc-insert-inv-prob",
                         DEFAULT_EM_FLOW_INSERT_INV_PROB);
@@ -3788,6 +3793,20 @@ dpif_netdev_set_config(struct dpif *dpif, const struct smap *other_config)
             VLOG_INFO("SMC cache is disabled");
         }
     }
+
+    bool pmd_rxq_assign_cyc = !strcmp(pmd_rxq_assign, "cycles");
+    if (!pmd_rxq_assign_cyc && strcmp(pmd_rxq_assign, "roundrobin")) {
+        VLOG_WARN("Unsupported Rxq to PMD assignment mode in pmd-rxq-assign. "
+                      "Defaulting to 'cycles'.");
+        pmd_rxq_assign_cyc = true;
+        pmd_rxq_assign = "cycles";
+    }
+    if (dp->pmd_rxq_assign_cyc != pmd_rxq_assign_cyc) {
+        dp->pmd_rxq_assign_cyc = pmd_rxq_assign_cyc;
+        VLOG_INFO("Rxq to PMD assignment mode changed to: \'%s\'.",
+                  pmd_rxq_assign);
+        dp_netdev_request_reconfigure(dp);
+    }
     return 0;
 }
 
@@ -4258,10 +4277,18 @@ rr_numa_list_populate(struct dp_netdev *dp, struct rr_numa_list *rr)
     }
 }
 
-/* Returns the next pmd from the numa node in
- * incrementing or decrementing order. */
+/*
+ * Returns the next pmd from the numa node.
+ *
+ * If 'updown' is 'true' it will alternate between selecting the next pmd in
+ * either an up or down walk, switching between up/down when the first or last
+ * core is reached. e.g. 1,2,3,3,2,1,1,2...
+ *
+ * If 'updown' is 'false' it will select the next pmd wrapping around when last
+ * core reached. e.g. 1,2,3,1,2,3,1,2...
+ */
 static struct dp_netdev_pmd_thread *
-rr_numa_get_pmd(struct rr_numa *numa)
+rr_numa_get_pmd(struct rr_numa *numa, bool updown)
 {
     int numa_idx = numa->cur_index;
 
@@ -4269,7 +4296,11 @@ rr_numa_get_pmd(struct rr_numa *numa)
         /* Incrementing through list of pmds. */
         if (numa->cur_index == numa->n_pmds-1) {
             /* Reached the last pmd. */
-            numa->idx_inc = false;
+            if (updown) {
+                numa->idx_inc = false;
+            } else {
+                numa->cur_index = 0;
+            }
         } else {
             numa->cur_index++;
         }
@@ -4332,9 +4363,6 @@ compare_rxq_cycles(const void *a, const void *b)
  * queues and marks the pmds as isolated.  Otherwise, assign non isolated
  * pmds to unpinned queues.
  *
- * If 'pinned' is false queues will be sorted by processing cycles they are
- * consuming and then assigned to pmds in round robin order.
- *
  * The function doesn't touch the pmd threads, it just stores the assignment
  * in the 'pmd' member of each rxq. */
 static void
@@ -4347,6 +4375,7 @@ rxq_scheduling(struct dp_netdev *dp, bool pinned) OVS_REQUIRES(dp->port_mutex)
     int n_rxqs = 0;
     struct rr_numa *numa = NULL;
     int numa_id;
+    bool assign_cyc = dp->pmd_rxq_assign_cyc;
 
     HMAP_FOR_EACH (port, node, &dp->ports) {
         if (!netdev_is_pmd(port->netdev)) {
@@ -4377,19 +4406,22 @@ rxq_scheduling(struct dp_netdev *dp, bool pinned) OVS_REQUIRES(dp->port_mutex)
                 } else {
                     rxqs = xrealloc(rxqs, sizeof *rxqs * (n_rxqs + 1));
                 }
-                /* Sum the queue intervals and store the cycle history. */
-                for (unsigned i = 0; i < PMD_RXQ_INTERVAL_MAX; i++) {
-                    cycle_hist += dp_netdev_rxq_get_intrvl_cycles(q, i);
-                }
-                dp_netdev_rxq_set_cycles(q, RXQ_CYCLES_PROC_HIST, cycle_hist);
 
+                if (assign_cyc) {
+                    /* Sum the queue intervals and store the cycle history. */
+                    for (unsigned i = 0; i < PMD_RXQ_INTERVAL_MAX; i++) {
+                        cycle_hist += dp_netdev_rxq_get_intrvl_cycles(q, i);
+                    }
+                    dp_netdev_rxq_set_cycles(q, RXQ_CYCLES_PROC_HIST,
+                                             cycle_hist);
+                }
                 /* Store the queue. */
                 rxqs[n_rxqs++] = q;
             }
         }
     }
 
-    if (n_rxqs > 1) {
+    if (n_rxqs > 1 && assign_cyc) {
         /* Sort the queues in order of the processing cycles
          * they consumed during their last pmd interval. */
         qsort(rxqs, n_rxqs, sizeof *rxqs, compare_rxq_cycles);
@@ -4413,7 +4445,7 @@ rxq_scheduling(struct dp_netdev *dp, bool pinned) OVS_REQUIRES(dp->port_mutex)
                          netdev_rxq_get_queue_id(rxqs[i]->rx));
                 continue;
             }
-            rxqs[i]->pmd = rr_numa_get_pmd(non_local_numa);
+            rxqs[i]->pmd = rr_numa_get_pmd(non_local_numa, assign_cyc);
             VLOG_WARN("There's no available (non-isolated) pmd thread "
                       "on numa node %d. Queue %d on port \'%s\' will "
                       "be assigned to the pmd on core %d "
@@ -4422,13 +4454,22 @@ rxq_scheduling(struct dp_netdev *dp, bool pinned) OVS_REQUIRES(dp->port_mutex)
                       netdev_rxq_get_name(rxqs[i]->rx),
                       rxqs[i]->pmd->core_id, rxqs[i]->pmd->numa_id);
         } else {
-        rxqs[i]->pmd = rr_numa_get_pmd(numa);
-        VLOG_INFO("Core %d on numa node %d assigned port \'%s\' "
-                  "rx queue %d (measured processing cycles %"PRIu64").",
-                  rxqs[i]->pmd->core_id, numa_id,
-                  netdev_rxq_get_name(rxqs[i]->rx),
-                  netdev_rxq_get_queue_id(rxqs[i]->rx),
-                  dp_netdev_rxq_get_cycles(rxqs[i], RXQ_CYCLES_PROC_HIST));
+            rxqs[i]->pmd = rr_numa_get_pmd(numa, assign_cyc);
+            if (assign_cyc) {
+                VLOG_INFO("Core %d on numa node %d assigned port \'%s\' "
+                          "rx queue %d "
+                          "(measured processing cycles %"PRIu64").",
+                          rxqs[i]->pmd->core_id, numa_id,
+                          netdev_rxq_get_name(rxqs[i]->rx),
+                          netdev_rxq_get_queue_id(rxqs[i]->rx),
+                          dp_netdev_rxq_get_cycles(rxqs[i],
+                                                   RXQ_CYCLES_PROC_HIST));
+            } else {
+                VLOG_INFO("Core %d on numa node %d assigned port \'%s\' "
+                          "rx queue %d.", rxqs[i]->pmd->core_id, numa_id,
+                          netdev_rxq_get_name(rxqs[i]->rx),
+                          netdev_rxq_get_queue_id(rxqs[i]->rx));
+            }
         }
     }
 
diff --git a/tests/pmd.at b/tests/pmd.at
index 4cae6c8c5..1f952f3c4 100644
--- a/tests/pmd.at
+++ b/tests/pmd.at
@@ -61,7 +61,8 @@ m4_define([CHECK_PMD_THREADS_CREATED], [
 ])
 
 m4_define([SED_NUMA_CORE_PATTERN], ["s/\(numa_id \)[[0-9]]*\( core_id \)[[0-9]]*:/\1<cleared>\2<cleared>:/"])
-m4_define([SED_NUMA_CORE_QUEUE_PATTERN], ["s/1 2 5 6/<group>/;s/0 3 4 7/<group>/"])
+m4_define([SED_NUMA_CORE_QUEUE_CYC_PATTERN], ["s/1 2 5 6/<group>/;s/0 3 4 7/<group>/"])
+m4_define([SED_NUMA_CORE_QUEUE_PQ_PATTERN], ["s/1 3 5 7/<group>/;s/0 2 4 6/<group>/"])
 m4_define([DUMMY_NUMA], [--dummy-numa="0,0,0,0"])
 
 AT_SETUP([PMD - creating a thread/add-port])
@@ -145,11 +146,18 @@ pmd thread numa_id <cleared> core_id <cleared>:
   port: p0                queue-id:  7  pmd usage: NOT AVAIL
 ])
 
+AT_CHECK([ovs-vsctl set Open_vSwitch . other_config:pmd-rxq-assign=cycles])
 TMP=$(cat ovs-vswitchd.log | wc -l | tr -d [[:blank:]])
 AT_CHECK([ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=0x3])
 CHECK_PMD_THREADS_CREATED([2], [], [+$TMP])
 
-AT_CHECK([ovs-appctl dpif-netdev/pmd-rxq-show | sed ':a;/AVAIL$/{N;s/\n//;ba;}' | parse_pmd_rxq_show_group | sed SED_NUMA_CORE_QUEUE_PATTERN], [0], [dnl
+AT_CHECK([ovs-appctl dpif-netdev/pmd-rxq-show | sed ':a;/AVAIL$/{N;s/\n//;ba;}' | parse_pmd_rxq_show_group | sed SED_NUMA_CORE_QUEUE_CYC_PATTERN], [0], [dnl
+port: p0 queue-id: <group>
+port: p0 queue-id: <group>
+])
+
+AT_CHECK([ovs-vsctl set Open_vSwitch . other_config:pmd-rxq-assign=roundrobin])
+AT_CHECK([ovs-appctl dpif-netdev/pmd-rxq-show | sed ':a;/AVAIL$/{N;s/\n//;ba;}' | parse_pmd_rxq_show_group | sed SED_NUMA_CORE_QUEUE_PQ_PATTERN], [0], [dnl
 port: p0 queue-id: <group>
 port: p0 queue-id: <group>
 ])
diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
index f05f616fe..66a8a3b4c 100644
--- a/vswitchd/vswitch.xml
+++ b/vswitchd/vswitch.xml
@@ -432,6 +432,30 @@
         </p>
       </column>
 
+      <column name="other_config" key="pmd-rxq-assign"
+              type='{"type": "string",
+                     "enum": ["set", ["cycles", "roundrobin"]]}'>
+        <p>
+          Specifies how RX queues will be automatically assigned to CPU cores.
+          Options:
+          <dl>
+            <dt><code>cycles</code></dt>
+            <dd>Rxqs will be sorted by order of measured processing cycles
+            before being assigned to CPU cores.</dd>
+            <dt><code>roundrobin</code></dt>
+            <dd>Rxqs will be round-robined across CPU cores.</dd>
+          </dl>
+        </p>
+        <p>
+          The default value is <code>cycles</code>.
+        </p>
+        <p>
+          Changing this value will affect an automatic re-assignment of Rxqs to
+          CPUs. Note: Rxqs mapped to CPU cores with
+          <code>pmd-rxq-affinity</code> are unaffected.
+        </p>
+      </column>
+
       <column name="other_config" key="n-handler-threads"
               type='{"type": "integer", "minInteger": 1}'>
         <p>