rculfhash: reorder cds_lfht for smaller cache footprint in fast-paths

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/rculfhash-internal.h b/rculfhash-internal.h
index cc146640a93336511e89412608d2ff48bff0946e..792e04da0304063041f57621091d6967c430b457 100644 (file)
--- a/rculfhash-internal.h
+++ b/rculfhash-internal.h
@@ -56,36 +56,10 @@ struct ht_items_count;
  * cookie to users.
  */
 struct cds_lfht {
-       unsigned long size;     /* always a power of 2, shared (RCU) */
-       int flags;
-
        /*
-        * We need to put the work threads offline (QSBR) when taking this
-        * mutex, because we use synchronize_rcu within this mutex critical
-        * section, which waits on read-side critical sections, and could
-        * therefore cause grace-period deadlock if we hold off RCU G.P.
-        * completion.
+        * Variables needed for the lookup, add and remove fast-paths.
         */
-       pthread_mutex_t resize_mutex;   /* resize mutex: add/del mutex */
-       pthread_attr_t *resize_attr;    /* Resize threads attributes */
-       unsigned int in_progress_resize, in_progress_destroy;
-       unsigned long resize_target;
-       int resize_initiated;
-       const struct rcu_flavor_struct *flavor;
-
-       long count;                     /* global approximate item count */
-       struct ht_items_count *split_count;     /* split item count */
-
-       /* memory management related fields are located at the end */
-       const struct cds_lfht_mm_type *mm;
-
-       unsigned long min_alloc_buckets_order;
-       unsigned long min_nr_alloc_buckets;
-       unsigned long max_nr_buckets;
-
-       struct cds_lfht_node *(*bucket_at)(struct cds_lfht *ht,
-                       unsigned long index);
-
+       unsigned long size;     /* always a power of 2, shared (RCU) */
        union {
                /*
                 * Contains the per order-index-level bucket node table.
@@ -115,6 +89,43 @@ struct cds_lfht {
                 */
                struct cds_lfht_node *tbl_mmap;
        };
+       /*
+        * bucket_at pointer is kept here to skip the extra level of
+        * dereference needed to get to "mm" (this is a fast-path).
+        */
+       struct cds_lfht_node *(*bucket_at)(struct cds_lfht *ht,
+                       unsigned long index);
+       /*
+        * End of variables needed for lookup fast-path.
+        */
+
+       struct ht_items_count *split_count;     /* split item count */
+       /*
+        * End of variables needed for add/remove fast-path.
+        */
+
+       /* Initial configuration items */
+       int flags;
+       unsigned long min_alloc_buckets_order;
+       unsigned long min_nr_alloc_buckets;
+       unsigned long max_nr_buckets;
+       const struct cds_lfht_mm_type *mm;      /* memory management plugin */
+       const struct rcu_flavor_struct *flavor; /* RCU flavor */
+
+       long count;                     /* global approximate item count */
+
+       /*
+        * We need to put the work threads offline (QSBR) when taking this
+        * mutex, because we use synchronize_rcu within this mutex critical
+        * section, which waits on read-side critical sections, and could
+        * therefore cause grace-period deadlock if we hold off RCU G.P.
+        * completion.
+        */
+       pthread_mutex_t resize_mutex;   /* resize mutex: add/del mutex */
+       pthread_attr_t *resize_attr;    /* Resize threads attributes */
+       unsigned int in_progress_resize, in_progress_destroy;
+       unsigned long resize_target;
+       int resize_initiated;
 };
 
 extern unsigned int fls_ulong(unsigned long x);