[ovs-dev] [PATCH 2/2] dpif-netdev: Store miniflow length in exact match cache

[Daniele Di Proietto]

This optimization is done to avoid calling count_1bits(), which, if the popcnt
istruction, is not available might is slow. popcnt may not be available
because:

- We are running on old hardware
- (more likely) We're using a generic build (i.e. packaged OVS from a distro),
  not tuned for the specific CPU

Signed-off-by: Daniele Di Proietto <ddiproie...@vmware.com>
---
This commit improves 1-flow UDP 64-bytes packets test throughput by 6%
(compiled without -march=native)
---
 lib/dpif-netdev.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 112cd5a..ea14838 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -129,6 +129,7 @@ struct netdev_flow_key {
 
 struct emc_entry {
     uint32_t hash;
+    uint32_t mf_len;
     struct netdev_flow_key mf;
     struct dp_netdev_flow *flow;
 };
@@ -398,6 +399,7 @@ emc_cache_init(struct emc_cache *flow_cache)
     for (i = 0; i < ARRAY_SIZE(flow_cache->entries); i++) {
         flow_cache->entries[i].flow = NULL;
         flow_cache->entries[i].hash = 0;
+        flow_cache->entries[i].mf_len = 0;
         miniflow_initialize(&flow_cache->entries[i].mf.flow,
                             flow_cache->entries[i].mf.buf);
     }
@@ -1171,11 +1173,10 @@ netdev_flow_key_size(uint32_t flow_u32s)
 /* Used to compare 'netdev_flow_key's (miniflows) in the exact match cache. */
 static inline bool
 netdev_flow_key_equal(const struct netdev_flow_key *a,
-                      const struct netdev_flow_key *b)
+                      const struct netdev_flow_key *b,
+                      uint32_t size)
 {
-    uint32_t size = count_1bits(a->flow.map);
-
-    return !memcmp(a, b, netdev_flow_key_size(size));
+    return !memcmp(a, b, size);
 }
 
 static inline void
@@ -1183,7 +1184,7 @@ netdev_flow_key_clone(struct netdev_flow_key *dst,
                       const struct netdev_flow_key *src,
                       uint32_t size)
 {
-    memcpy(dst, src, netdev_flow_key_size(size));
+    memcpy(dst, src, size);
 }
 
 static inline bool
@@ -1217,8 +1218,11 @@ emc_change_entry(struct emc_entry *ce, struct 
dp_netdev_flow *flow,
         }
     }
     if (mf) {
-        netdev_flow_key_clone(&ce->mf, mf, count_1bits(mf->flow.map));
+        uint32_t mf_len = netdev_flow_key_size(count_1bits(mf->flow.map));
+
+        netdev_flow_key_clone(&ce->mf, mf, mf_len);
         ce->hash = hash;
+        ce->mf_len = mf_len;
     }
 }
 
@@ -1232,7 +1236,8 @@ emc_insert(struct emc_cache *cache, const struct miniflow 
*mf, uint32_t hash,
     EMC_FOR_EACH_POS_WITH_HASH(cache, current_entry, hash) {
         if (current_entry->hash == hash
             && netdev_flow_key_equal(&current_entry->mf,
-                                     miniflow_to_netdev_flow_key(mf))) {
+                                     miniflow_to_netdev_flow_key(mf),
+                                     current_entry->mf_len)) {
 
             /* We found the entry with the 'mf' miniflow */
             emc_change_entry(current_entry, flow, NULL, 0);
@@ -1263,7 +1268,8 @@ emc_lookup(struct emc_cache *cache, const struct miniflow 
*mf, uint32_t hash)
     EMC_FOR_EACH_POS_WITH_HASH(cache, current_entry, hash) {
         if (current_entry->hash == hash && emc_entry_alive(current_entry)
             && netdev_flow_key_equal(&current_entry->mf,
-                                     miniflow_to_netdev_flow_key(mf))) {
+                                     miniflow_to_netdev_flow_key(mf),
+                                     current_entry->mf_len)) {
 
             /* We found the entry with the 'mf' miniflow */
             return current_entry->flow;
-- 
2.1.0.rc1

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