ck_epoch: Read-side latency improvements on x86.

include/ck_epoch.h

@@ -100,8 +100,15 @@ ck_epoch_begin(ck_epoch_t *epoch, ck_epoch_record_t *record)
 		 * For this reason, store to load serialization is necessary.
 		 */
 		ck_pr_store_uint(&record->epoch, g_epoch);
+
+#if defined(__x86__) || defined(__x86_64__)
+		ck_pr_fas_uint(&record->active, 1);
+		ck_pr_fence_atomic_load();
+#else
 		ck_pr_store_uint(&record->active, 1);
 		ck_pr_fence_store_load();
+#endif
+
 		return;
 	}