netdev-dpdk: dfc_process optimization by prefetching EMC entry.

It is observed that the throughput of multi-flow is worse than single-flow
in the EMC NIC to NIC cases. It is because CPU cache-miss increasing in EMC
lookup. Each flow need load at least one EMC entry to CPU cache(several
cache lines) and compare it with packet miniflow.
This patch improve it by prefetching EMC entry in advance. Hash value can
be obtained from dpdk rss hash, so this step can be advanced ahead of
miniflow_extract() and prefetch EMC entry there. The prefetching size is
defined as ROUND_UP(128,CACHE_LINE_SIZE), which can cover majority traffic
including TCP/UDP protocol and need 2 cache lines in most modern CPU.
Performance test was run in some arm platform. 1000/10000 flows NIC2NIC
test achieved around 10% throughput improvement in thunderX2(aarch64
platform).

Signed-off-by: Yanqin Wei <Yanqin.Wei@arm.com>
Reviewed-by: Gavin Hu <Gavin.Hu@arm.com>
Signed-off-by: 0-day Robot <robot@bytheb.org>

lib/dpif-netdev.c

@@ -189,6 +189,9 @@ struct netdev_flow_key {
 #define DEFAULT_EM_FLOW_INSERT_MIN (UINT32_MAX /                     \
                                     DEFAULT_EM_FLOW_INSERT_INV_PROB)
 
+/* DEFAULT_EMC_PREFETCH_SIZE can cover majority traffic including TCP/UDP protocol*/
+#define DEFAULT_EMC_PREFETCH_SIZE ROUND_UP(128,CACHE_LINE_SIZE)
+
 struct emc_entry {
     struct dp_netdev_flow *flow;
     struct netdev_flow_key key;   /* key.hash used for emc hash value. */
@@ -6166,40 +6169,46 @@ dp_netdev_upcall(struct dp_netdev_pmd_thread *pmd, struct dp_packet *packet_,
 }
 
 static inline uint32_t
-dpif_netdev_packet_get_rss_hash_orig_pkt(struct dp_packet *packet,
-                                const struct miniflow *mf)
+dpif_netdev_packet_get_packet_rss_hash(struct dp_packet *packet,
+                                bool md_is_valid)
 {
-    uint32_t hash;
+    uint32_t hash,recirc_depth;
 
-    if (OVS_LIKELY(dp_packet_rss_valid(packet))) {
-        hash = dp_packet_get_rss_hash(packet);
-    } else {
-        hash = miniflow_hash_5tuple(mf, 0);
+    hash = dp_packet_get_rss_hash(packet);
+
+    if(md_is_valid)
+    {
+        /* The RSS hash must account for the recirculation depth to avoid
+         * collisions in the exact match cache */
+        recirc_depth = *recirc_depth_get_unsafe();
+        if (OVS_UNLIKELY(recirc_depth)) {
+            hash = hash_finish(hash, recirc_depth);
+        }
         dp_packet_set_rss_hash(packet, hash);
     }
 
     return hash;
 }
 
 static inline uint32_t
-dpif_netdev_packet_get_rss_hash(struct dp_packet *packet,
-                                const struct miniflow *mf)
+dpif_netdev_packet_get_hash_5tuple(struct dp_packet *packet,
+                                const struct miniflow *mf,
+                                bool md_is_valid)
 {
-    uint32_t hash, recirc_depth;
+    uint32_t hash,recirc_depth;
 
-    if (OVS_LIKELY(dp_packet_rss_valid(packet))) {
-        hash = dp_packet_get_rss_hash(packet);
-    } else {
-        hash = miniflow_hash_5tuple(mf, 0);
-        dp_packet_set_rss_hash(packet, hash);
-    }
+    hash = miniflow_hash_5tuple(mf, 0);
+    dp_packet_set_rss_hash(packet, hash);
 
-    /* The RSS hash must account for the recirculation depth to avoid
-     * collisions in the exact match cache */
-    recirc_depth = *recirc_depth_get_unsafe();
-    if (OVS_UNLIKELY(recirc_depth)) {
-        hash = hash_finish(hash, recirc_depth);
-        dp_packet_set_rss_hash(packet, hash);
+    if(md_is_valid)
+    {
+        /* The RSS hash must account for the recirculation depth to avoid
+         * collisions in the exact match cache */
+        recirc_depth = *recirc_depth_get_unsafe();
+        if (OVS_UNLIKELY(recirc_depth)) {
+            hash = hash_finish(hash, recirc_depth);
+            dp_packet_set_rss_hash(packet, hash);
+        }
     }
     return hash;
 }
@@ -6390,6 +6399,7 @@ dfc_processing(struct dp_netdev_pmd_thread *pmd,
     bool smc_enable_db;
     size_t map_cnt = 0;
     bool batch_enable = true;
+    bool is_5tuple_hash_needed;
 
     atomic_read_relaxed(&pmd->dp->smc_enable_db, &smc_enable_db);
     pmd_perf_update_counter(&pmd->perf_stats,
@@ -6436,16 +6446,29 @@ dfc_processing(struct dp_netdev_pmd_thread *pmd,
             }
         }
 
-        miniflow_extract(packet, &key->mf);
-        key->len = 0; /* Not computed yet. */
         /* If EMC and SMC disabled skip hash computation */
         if (smc_enable_db == true || cur_min != 0) {
-            if (!md_is_valid) {
-                key->hash = dpif_netdev_packet_get_rss_hash_orig_pkt(packet,
-                        &key->mf);
-            } else {
-                key->hash = dpif_netdev_packet_get_rss_hash(packet, &key->mf);
+            if (OVS_LIKELY(dp_packet_rss_valid(packet)))
+            {
+                is_5tuple_hash_needed = false;
+                key->hash = dpif_netdev_packet_get_packet_rss_hash(packet,md_is_valid);
+                if (cur_min) {
+                    ovs_prefetch_range(&cache->emc_cache.entries[key->hash & EM_FLOW_HASH_MASK],
+                                   DEFAULT_EMC_PREFETCH_SIZE);
+                }
             }
+            else
+                is_5tuple_hash_needed = true;
+        }
+        else
+            is_5tuple_hash_needed = false;
+
+        miniflow_extract(packet, &key->mf);
+        key->len = 0; /* Not computed yet. */
+
+        /* If 5tuple hash is needed */
+        if (is_5tuple_hash_needed) {
+            key->hash = dpif_netdev_packet_get_hash_5tuple(packet, &key->mf, md_is_valid);
         }
         if (cur_min) {
             flow = emc_lookup(&cache->emc_cache, key);