ofproto-dpif: Process multiple batches of upcalls in a single poll loop.

This yields a 27% improvement in netperf CRR results in my tests
versus the previous commit, which is a 52% improvement versus
the baseline from just before the poll_fd_woke() optimization was
removed.

diff --git a/ofproto/ofproto-dpif.c b/ofproto/ofproto-dpif.c
index c41f4db..4cf5370 100644 (file)
--- a/ofproto/ofproto-dpif.c
+++ b/ofproto/ofproto-dpif.c
@@ -415,9 +415,7 @@ static bool is_admissible(struct ofproto_dpif *, const struct flow *,
 
 /* Upcalls. */
 #define FLOW_MISS_MAX_BATCH 50
-static void handle_upcall(struct ofproto_dpif *, struct dpif_upcall *);
-static void handle_miss_upcalls(struct ofproto_dpif *,
-                                struct dpif_upcall *, size_t n);
+static int handle_upcalls(struct ofproto_dpif *, unsigned int max_batch);
 
 /* Flow expiration. */
 static int expire(struct ofproto_dpif *);
@@ -587,40 +585,36 @@ static int
 run(struct ofproto *ofproto_)
 {
     struct ofproto_dpif *ofproto = ofproto_dpif_cast(ofproto_);
-    struct dpif_upcall misses[FLOW_MISS_MAX_BATCH];
     struct ofport_dpif *ofport;
     struct ofbundle *bundle;
-    size_t n_misses;
-    int i;
+    unsigned int work;
 
     if (!clogged) {
         complete_operations(ofproto);
     }
     dpif_run(ofproto->dpif);
 
-    n_misses = 0;
-    for (i = 0; i < FLOW_MISS_MAX_BATCH; i++) {
-        struct dpif_upcall *upcall = &misses[n_misses];
-        int error;
-
-        error = dpif_recv(ofproto->dpif, upcall);
-        if (error) {
-            if (error == ENODEV && n_misses == 0) {
-                return error;
-            }
+    /* Handle one or more batches of upcalls, until there's nothing left to do
+     * or until we do a fixed total amount of work.
+     *
+     * We do work in batches because it can be much cheaper to set up a number
+     * of flows and fire off their patches all at once.  We do multiple batches
+     * because in some cases handling a packet can cause another packet to be
+     * queued almost immediately as part of the return flow.  Both
+     * optimizations can make major improvements on some benchmarks and
+     * presumably for real traffic as well. */
+    work = 0;
+    while (work < FLOW_MISS_MAX_BATCH) {
+        int retval = handle_upcalls(ofproto, FLOW_MISS_MAX_BATCH - work);
+        if (retval < 0) {
+            return -retval;
+        } else if (!retval) {
             break;
-        }
-
-        if (upcall->type == DPIF_UC_MISS) {
-            /* Handle it later. */
-            n_misses++;
         } else {
-            handle_upcall(ofproto, upcall);
+            work += retval;
         }
     }
 
-    handle_miss_upcalls(ofproto, misses, n_misses);
-
     if (timer_expired(&ofproto->next_expiration)) {
         int delay = expire(ofproto);
         timer_set_duration(&ofproto->next_expiration, delay);
@@ -2341,23 +2335,49 @@ handle_userspace_upcall(struct ofproto_dpif *ofproto,
     }
 }
 
-static void
-handle_upcall(struct ofproto_dpif *ofproto, struct dpif_upcall *upcall)
+static int
+handle_upcalls(struct ofproto_dpif *ofproto, unsigned int max_batch)
 {
-    switch (upcall->type) {
-    case DPIF_UC_ACTION:
-        handle_userspace_upcall(ofproto, upcall);
-        break;
+    struct dpif_upcall misses[FLOW_MISS_MAX_BATCH];
+    int n_misses;
+    int i;
 
-    case DPIF_UC_MISS:
-        /* The caller handles these. */
-        NOT_REACHED();
+    assert (max_batch <= FLOW_MISS_MAX_BATCH);
 
-    case DPIF_N_UC_TYPES:
-    default:
-        VLOG_WARN_RL(&rl, "upcall has unexpected type %"PRIu32, upcall->type);
-        break;
+    n_misses = 0;
+    for (i = 0; i < max_batch; i++) {
+        struct dpif_upcall *upcall = &misses[n_misses];
+        int error;
+
+        error = dpif_recv(ofproto->dpif, upcall);
+        if (error) {
+            if (error == ENODEV && n_misses == 0) {
+                return -ENODEV;
+            }
+            break;
+        }
+
+        switch (upcall->type) {
+        case DPIF_UC_ACTION:
+            handle_userspace_upcall(ofproto, upcall);
+            break;
+
+        case DPIF_UC_MISS:
+            /* Handle it later. */
+            n_misses++;
+            break;
+
+        case DPIF_N_UC_TYPES:
+        default:
+            VLOG_WARN_RL(&rl, "upcall has unexpected type %"PRIu32,
+                         upcall->type);
+            break;
+        }
     }
+
+    handle_miss_upcalls(ofproto, misses, n_misses);
+
+    return i;
 }
 \f
 /* Flow expiration. */