rculfhash: spawn only number of threads required for resize

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

diff --git a/rculfhash.c b/rculfhash.c
index 42501a1f030c6ee29fb0c40e5fdc02394da06992..b11bbf41c5308e4505fbea492bae09cb5d622b74 100644 (file)
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -180,7 +180,8 @@
 /*
  * Minimum number of dummy nodes to touch per thread to parallelize grow/shrink.
  */
-#define MIN_PARTITION_PER_THREAD       4096
+#define MIN_PARTITION_PER_THREAD_ORDER 12
+#define MIN_PARTITION_PER_THREAD       (1UL << MIN_PARTITION_PER_THREAD_ORDER)
 
 #ifndef min
 #define min(a, b)      ((a) < (b) ? (a) : (b))
@@ -914,26 +915,33 @@ void partition_resize_helper(struct cds_lfht *ht, unsigned long i,
 {
        unsigned long partition_len;
        struct partition_resize_work *work;
-       int cpu, ret;
+       int thread, ret;
+       unsigned long nr_threads;
        pthread_t *thread_id;
 
-       /* Note: nr_cpus_mask + 1 is always power of 2 */
-       partition_len = len >> get_count_order_ulong(nr_cpus_mask + 1);
-       work = calloc(nr_cpus_mask + 1, sizeof(*work));
-       thread_id = calloc(nr_cpus_mask + 1, sizeof(*thread_id));
+       /*
+        * Note: nr_cpus_mask + 1 is always power of 2.
+        * We spawn just the number of threads we need to satisfy the minimum
+        * partition size, up to the number of CPUs in the system.
+        */
+       nr_threads = min(nr_cpus_mask + 1,
+                        len >> MIN_PARTITION_PER_THREAD_ORDER);
+       partition_len = len >> get_count_order_ulong(nr_threads);
+       work = calloc(nr_threads, sizeof(*work));
+       thread_id = calloc(nr_threads, sizeof(*thread_id));
        assert(work);
-       for (cpu = 0; cpu < nr_cpus_mask + 1; cpu++) {
-               work[cpu].ht = ht;
-               work[cpu].i = i;
-               work[cpu].len = partition_len;
-               work[cpu].start = cpu * partition_len;
-               work[cpu].fct = fct;
-               ret = pthread_create(&thread_id[cpu], ht->resize_attr,
-                       partition_resize_thread, &work[cpu]);
+       for (thread = 0; thread < nr_threads; thread++) {
+               work[thread].ht = ht;
+               work[thread].i = i;
+               work[thread].len = partition_len;
+               work[thread].start = thread * partition_len;
+               work[thread].fct = fct;
+               ret = pthread_create(&thread_id[thread], ht->resize_attr,
+                       partition_resize_thread, &work[thread]);
                assert(!ret);
        }
-       for (cpu = 0; cpu < nr_cpus_mask + 1; cpu++) {
-               ret = pthread_join(thread_id[cpu], NULL);
+       for (thread = 0; thread < nr_threads; thread++) {
+               ret = pthread_join(thread_id[thread], NULL);
                assert(!ret);
        }
        free(work);
@@ -979,7 +987,7 @@ void init_table_populate(struct cds_lfht *ht, unsigned long i,
                         unsigned long len)
 {
        assert(nr_cpus_mask != -1);
-       if (nr_cpus_mask < 0 || len < (nr_cpus_mask + 1) * MIN_PARTITION_PER_THREAD) {
+       if (nr_cpus_mask < 0 || len < 2 * MIN_PARTITION_PER_THREAD) {
                ht->cds_lfht_rcu_thread_online();
                init_table_populate_partition(ht, i, 0, len);
                ht->cds_lfht_rcu_thread_offline();
@@ -1082,7 +1090,7 @@ void remove_table(struct cds_lfht *ht, unsigned long i, unsigned long len)
 {
 
        assert(nr_cpus_mask != -1);
-       if (nr_cpus_mask < 0 || len < (nr_cpus_mask + 1) * MIN_PARTITION_PER_THREAD) {
+       if (nr_cpus_mask < 0 || len < 2 * MIN_PARTITION_PER_THREAD) {
                ht->cds_lfht_rcu_thread_online();
                remove_table_partition(ht, i, 0, len);
                ht->cds_lfht_rcu_thread_offline();