diff --git a/NEWS b/NEWS
index 743528e..7d40374 100644
--- a/NEWS
+++ b/NEWS
@@ -47,6 +47,8 @@ Post-v2.8.0
      * Commands ovs-appctl dpif-netdev/pmd-*-show can now work on a single PMD
      * Detailed PMD performance metrics available with new command
          ovs-appctl dpif-netdev/pmd-perf-show
+     * Supervision of PMD performance metrics and logging of suspicious
+       iterations
    - vswitchd:
      * Datapath IDs may now be specified as 0x1 (etc.) instead of 16 digits.
      * Configuring a controller, or unconfiguring all controllers, now deletes
diff --git a/lib/dpif-netdev-perf.c b/lib/dpif-netdev-perf.c
index e0ef15d..259a6c8 100644
--- a/lib/dpif-netdev-perf.c
+++ b/lib/dpif-netdev-perf.c
@@ -24,6 +24,23 @@
 
 VLOG_DEFINE_THIS_MODULE(pmd_perf);
 
+#define ITER_US_THRESHOLD 250   /* Warning threshold for iteration duration
+                                   in microseconds. */
+#define VHOST_QUEUE_FULL 128    /* Size of the virtio TX queue. */
+#define LOG_IT_BEFORE 5         /* Number of iteration to log before
+                                   suspicious iteration. */
+#define LOG_IT_AFTER 5          /* Number of iteration to log after
+                                   suspicious iteration. */
+
+bool log_on = false;
+static uint32_t log_it_before = LOG_IT_BEFORE;
+static uint32_t log_it_after = LOG_IT_AFTER;
+static uint32_t log_us_thr = ITER_US_THRESHOLD;
+uint32_t log_q_thr = VHOST_QUEUE_FULL;
+uint64_t iter_cycle_threshold;
+
+static struct vlog_rate_limit latency_rl = VLOG_RATE_LIMIT_INIT(600, 600);
+
 #ifdef DPDK_NETDEV
 static uint64_t
 get_tsc_hz(void)
@@ -124,6 +141,8 @@ pmd_perf_stats_init(struct pmd_perf_stats *s)
     histogram_walls_set_log(&s->cycles_per_upcall, 1000, 1000000);
     histogram_walls_set_log(&s->max_vhost_qfill, 0, 512);
     s->start_ms = time_msec();
+    s->log_begin_it = UINT64_MAX;
+    s->log_end_it = UINT64_MAX;
 }
 
 void
@@ -362,6 +381,8 @@ pmd_perf_stats_clear__(struct pmd_perf_stats *s)
     history_init(&s->milliseconds);
     s->start_ms = time_msec();
     s->milliseconds.sample[0].timestamp = s->start_ms;
+    s->log_begin_it = UINT64_MAX;
+    s->log_end_it = UINT64_MAX;
     /* Clearing finished. */
     s->clear = false;
 }
@@ -387,3 +408,124 @@ non_pmd_perf_stats_clear(struct pmd_perf_stats *s)
 {
     pmd_perf_stats_clear__(s);
 }
+
+void
+pmd_perf_log_suspicious_iteration(struct pmd_perf_stats *s,
+                                     uint64_t cycles,
+                                     char *reason)
+{
+    VLOG_WARN_RL(&latency_rl,
+                 "Suspicious iteration (%s): tsc=%"PRIu64
+                 " duration=%"PRIu64" us\n",
+                 reason, s->current.timestamp,
+                 (1000000L * cycles) / get_tsc_hz());
+    if (log_it_before + log_it_after > 0) {
+        if (s->log_begin_it == UINT64_MAX) {
+            s->log_begin_it =
+                    (s->iterations.idx + HISTORY_LEN - log_it_before)
+                        % HISTORY_LEN;
+        }
+        s->log_end_it =
+                (s->iterations.idx + log_it_after) % HISTORY_LEN;
+    }
+}
+
+void
+pmd_perf_log_iteration_neighborhood(struct pmd_perf_stats *s)
+{
+    struct ds log = DS_EMPTY_INITIALIZER;
+    pmd_perf_format_iteration_history(&log, s,
+            (s->log_end_it + HISTORY_LEN - s->log_begin_it) % HISTORY_LEN);
+    VLOG_WARN_RL(&latency_rl,
+                 "Neighborhood of suspicious iteration:\n"
+                 "%s", ds_cstr(&log));
+    ds_destroy(&log);
+    s->log_end_it = s->log_begin_it = UINT64_MAX;
+    if (log_it_before > 100 || log_it_after > 100) {
+        /* Reset to safe default values to avoid disturbance. */
+        log_it_before = LOG_IT_BEFORE;
+        log_it_after = LOG_IT_AFTER;
+    }
+}
+
+void
+pmd_perf_log_set_cmd(struct unixctl_conn *conn,
+                 int argc, const char *argv[],
+                 void *aux OVS_UNUSED)
+{
+    int it_before, it_after, us_thr, q_thr;
+    bool on;
+    bool usage = false;
+
+    on = log_on;
+    it_before = log_it_before;
+    it_after = log_it_after;
+    q_thr = log_q_thr;
+    us_thr = log_us_thr;
+
+    while (argc > 1) {
+        if (!strcmp(argv[1], "on")) {
+            on = true;
+            argc--;
+            argv++;
+        } else if (!strcmp(argv[1], "off")) {
+            on = false;
+            argc--;
+            argv++;
+        } else if (!strcmp(argv[1], "-a")) {
+            it_after = strtol(argv[2], NULL, 10);
+            if (it_after < 0) {
+                it_after = 0;
+            } else if (it_before + it_after > HISTORY_LEN-1) {
+                it_after = HISTORY_LEN-1 - it_before;
+            }
+            argc -= 2;
+            argv += 2;
+        } else if (!strcmp(argv[1], "-b")) {
+            it_before = strtol(argv[2], NULL, 10);
+            if (it_before < 0) {
+                it_before = 0;
+            } else if (it_before > HISTORY_LEN-10) {
+                it_before = HISTORY_LEN-10;
+            }
+            argc -= 2;
+            argv += 2;
+        } else if (!strcmp(argv[1], "-q")) {
+            q_thr = strtol(argv[2], NULL, 10);
+            if (q_thr < 0) {
+                q_thr = 0;
+            }
+            argc -= 2;
+            argv += 2;
+        } else if (!strcmp(argv[1], "-us")) {
+            us_thr = strtol(argv[2], NULL, 10);
+            if (us_thr < 0) {
+                us_thr = 0;
+            }
+            argc -= 2;
+            argv += 2;
+        } else {
+            usage = true;
+            break;
+        }
+    }
+
+    if (usage) {
+        unixctl_command_reply_error(conn,
+                "Usage: ovs-appctl dpif-netdev/pmd-perf-log-set "
+                "[on|off] [-b before] [-a after] [-us usec] [-q qlen]");
+        return;
+    }
+
+    VLOG_INFO("pmd-perf-log-set: %s, before=%d, after=%d, us_thr=%d,"
+              " q_thr=%d\n",
+              on ? "on" : "off", it_before, it_after, us_thr, q_thr);
+    log_on = on;
+    log_it_before = it_before;
+    log_it_after = it_after;
+    log_q_thr = q_thr;
+    log_us_thr = us_thr;
+    iter_cycle_threshold = (log_us_thr * get_tsc_hz()) / 1000000L;
+
+    unixctl_command_reply(conn, "");
+}
diff --git a/lib/dpif-netdev-perf.h b/lib/dpif-netdev-perf.h
index 7a89c40..aa55c68 100644
--- a/lib/dpif-netdev-perf.h
+++ b/lib/dpif-netdev-perf.h
@@ -160,8 +160,12 @@ struct pmd_perf_stats {
     struct histogram max_vhost_qfill;
     /* Iteration history buffer. */
     struct history iterations;
-    /* Millisecond hitory buffer. */
+    /* Millisecond history buffer. */
     struct history milliseconds;
+    /* Start of iteration range to log. */
+    uint64_t log_begin_it;
+    /* End of iteration range to log. */
+    uint64_t log_end_it;
 };
 
 /* Support for accurate timing of PMD execution on TSC clock cycle level.
@@ -322,6 +326,17 @@ history_store(struct history *h, struct iter_stats *is)
     return history_next(h);
 }
 
+/* Data and function related to logging of suspicious iterations. */
+
+extern bool log_on;
+extern uint32_t log_q_thr;
+extern uint64_t iter_cycle_threshold;
+
+void pmd_perf_log_suspicious_iteration(struct pmd_perf_stats *s,
+                                       uint64_t cycles,
+                                       char *reason);
+void pmd_perf_log_iteration_neighborhood(struct pmd_perf_stats *s);
+
 /* Functions recording PMD metrics per iteration. */
 
 static inline void
@@ -351,6 +366,7 @@ pmd_perf_end_iteration(struct pmd_perf_stats *s, int rx_packets,
     uint64_t now_tsc = cycles_counter_update(s);
     struct iter_stats *cum_ms;
     uint64_t cycles, cycles_per_pkt = 0;
+    char *reason = NULL;
 
     if (OVS_UNLIKELY(s->current.timestamp == 0)) {
         /* Stats were cleared during the ongoing iteration. */
@@ -404,6 +420,23 @@ pmd_perf_end_iteration(struct pmd_perf_stats *s, int rx_packets,
     cum_ms->batches += s->current.batches;
     cum_ms->max_vhost_qfill += s->current.max_vhost_qfill;
 
+    if (log_on) {
+        /* Log suspicious iterations. */
+        if (cycles > iter_cycle_threshold) {
+            reason = "Excessive total cycles";
+        } else if (s->current.max_vhost_qfill >= log_q_thr) {
+            reason = "Vhost RX queue full";
+        }
+        if (OVS_UNLIKELY(reason)) {
+            pmd_perf_log_suspicious_iteration(s, cycles, reason);
+        }
+
+        /* Log iteration stats interval when required. */
+        if (OVS_UNLIKELY(s->log_end_it == s->iterations.idx)) {
+            pmd_perf_log_iteration_neighborhood(s);
+        }
+    }
+
     /* Store in iteration history. */
     history_store(&s->iterations, &s->current);
     if (now_tsc > s->next_check_tsc) {
@@ -426,7 +459,7 @@ pmd_perf_end_iteration(struct pmd_perf_stats *s, int rx_packets,
     }
 }
 
-/* Functions for formatting the output of commands. */
+/* Formatting the output of commands. */
 
 struct pmd_perf_params {
     int command_type;
@@ -443,6 +476,9 @@ void pmd_perf_format_iteration_history(struct ds *str,
                                        int n_iter);
 void pmd_perf_format_ms_history(struct ds *str, struct pmd_perf_stats *s,
                                 int n_ms);
+void pmd_perf_log_set_cmd(struct unixctl_conn *conn,
+                          int argc, const char *argv[],
+                          void *aux OVS_UNUSED);
 
 #ifdef  __cplusplus
 }
diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index f5931bf..b493216 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -1095,7 +1095,7 @@ dpif_netdev_pmd_info(struct unixctl_conn *conn, int argc, const char *argv[],
     ovs_mutex_lock(&dp_netdev_mutex);
 
     while (argc > 1) {
-        if (!strcmp(argv[1], "-pmd") && argc >= 3) {
+        if (!strcmp(argv[1], "-pmd") && argc > 2) {
             if (str_to_uint(argv[2], 10, &core_id)) {
                 filter_on_pmd = true;
             }
@@ -1218,6 +1218,11 @@ dpif_netdev_init(void)
     unixctl_command_register("dpif-netdev/pmd-rxq-rebalance", "[dp]",
                              0, 1, dpif_netdev_pmd_rebalance,
                              NULL);
+    unixctl_command_register("dpif-netdev/pmd-perf-log-set",
+                             "on|off [-b before] [-a after] "
+                             "[-us usec] [-q qlen]",
+                             0, 10, pmd_perf_log_set_cmd,
+                             NULL);
     return 0;
 }
 
diff --git a/lib/netdev-dpif-unixctl.man b/lib/netdev-dpif-unixctl.man
index 53f4c51..82e372f 100644
--- a/lib/netdev-dpif-unixctl.man
+++ b/lib/netdev-dpif-unixctl.man
@@ -70,7 +70,7 @@ This raw recorded data is used threefold:
 
 The command options are
 
-    \fB-nh\fR:                  Suppress the histograms
+    \fB-nh\fR:            Suppress the histograms
     \fB-it\fR \fIiter_len\fR:   Display the last iter_len iteration stats
     \fB-ms\fR \fIms_len\fR:     Display the last ms_len millisecond stats
 
@@ -101,10 +101,53 @@ To reset the counters and start a new measurement use
 .
 .IP "\fBdpif-netdev/pmd-stats-clear\fR [\fIdp\fR]"
 Resets to zero the per pmd thread performance numbers shown by the
-\fBdpif-netdev/pmd-stats-show\fR and \Bdpif-netdev/pmd-perf-show \fR commands.
+\fBdpif-netdev/pmd-stats-show\fR and \fBdpif-netdev/pmd-perf-show\fR commands.
 It will NOT reset datapath or bridge statistics, only the values shown by
 the above commands.
 .
+.IP "\fBdpif-netdev/pmd-perf-log-set\fR \fBon\fR|\fBoff\fR \
+ [\fB-b\fR \fIbefore\fR] [\fB-a\fR \fIafter\fR] [\fB-us\fR \fIusec\fR] \
+ [\fB-q\fR \fIqlen\fR]"
+.
+The userspace "netdev" datapath is able to supervise the PMD performance
+metrics and detect iterations with suspicious statistics according to the
+following criteria:
+
+- The iteration lasts longer than \fIusec\fR microseconds (default 250).
+  This can be used to capture events where a PMD is blocked or
+  interrupted for such a period of time that there is a risk for
+  dropped packets on any of its Rx queues.
+
+- The max vhost qlen exceeds a threshold \fIqlen\fR (default 128). This can
+  be used to infer virtio queue overruns and dropped packets inside a VM,
+  which are not visible in OVS otherwise.
+
+Such suspicious iterations can be logged together with their iteration
+statistics in the \fBovs-vswitchd.log\fR to be able to correlate them to
+packet drop or other events outside OVS.
+
+The above command enables (\fBon\fR) or disables (\fBoff\fR) supervision and
+logging at run-time and can be used to adjust the above thresholds for
+detecting suspicious iterations. By default supervision and logging is
+disabled.
+
+The command options are:
+
+    \fB-b\fR \fIbefore\fR:
+        The number of iterations before the suspicious iteration to be logged (default 5).
+    \fB-a\fR \fIafter\fR:
+        The number of iterations after the suspicious iteration to be logged (default 5).
+    \fB-q\fR \fIqlen\fR:
+        Suspicious vhost queue fill level threshold. Increase this to 512 if
+        the Qemu supports 1024 virtio queue length (default 128).
+    \fB-us\fR \fIusec\fR:
+        change the duration threshold for a suspicious iteration (default 250 us).
+
+If more than 100 iterations before or after a suspicious iteration have
+been looged once, OVS falls back to the safe default values (5/5) to
+avoid that logging itself causes continuos further suspicious iterations
+and continuous logging.
+.
 .IP "\fBdpif-netdev/pmd-rxq-show\fR [\fB-pmd\fR \fIcore\fR] [\fIdp\fR]"
 For one or all pmd threads of the datapath \fIdp\fR show the list of queue-ids
 with port names, which this thread polls.
