Introduced a new timer based innodb thread concurrency. A new

parameter innodb_thread_concurrency_timer_based is used to
get this new feature (it is set by default). The new feature
is only available on platforms where atomic instructions are
available.

storage/innobase/handler/ha_innodb.cc

@@ -148,6 +148,9 @@ long innobase_max_merged_io = 64;
 /* Number of background IO threads for read and write. */
 long innobase_read_io_threads, innobase_write_io_threads;
 
+/* Use timer based InnoDB concurrency throttling flag */
+static my_bool innobase_thread_concurrency_timer_based;
+
 /* The following counter is used to convey information to InnoDB
 about server activity: in selects it is not sensible to call
 srv_active_wake_master_thread after each fetch or search, we only do
@@ -1602,6 +1605,9 @@ innobase_init(
 	srv_n_log_files = (ulint) innobase_log_files_in_group;
 	srv_log_file_size = (ulint) innobase_log_file_size;
 
+        srv_thread_concurrency_timer_based =
+          (ibool) innobase_thread_concurrency_timer_based;
+
 #ifdef UNIV_LOG_ARCHIVE
 	srv_log_archive_on = (ulint) innobase_log_archive;
 #endif /* UNIV_LOG_ARCHIVE */
@@ -8236,6 +8242,12 @@ static MYSQL_SYSVAR_ULONG(sync_spin_loops, srv_n_spin_wait_rounds,
   "Count of spin-loop rounds in InnoDB mutexes",
   NULL, NULL, 20L, 0L, ~0L, 0);
 
+static MYSQL_SYSVAR_BOOL(thread_concurrency_timer_based,
+                         innobase_thread_concurrency_timer_based,
+                         PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
+  "Use InnoDB timer based concurrency throttling. ",
+  NULL, NULL, TRUE);
+
 static MYSQL_SYSVAR_ULONG(thread_concurrency, srv_thread_concurrency,
   PLUGIN_VAR_RQCMDARG,
   "Helps in performance tuning in heavily concurrent environments. Sets the maximum number of threads allowed inside InnoDB. Value 0 will disable the thread throttling.",
@@ -8278,6 +8290,7 @@ static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(read_io_threads),
   MYSQL_SYSVAR(write_io_threads),
   MYSQL_SYSVAR(max_merged_io),
+  MYSQL_SYSVAR(thread_concurrency_timer_based),
   MYSQL_SYSVAR(file_per_table),
   MYSQL_SYSVAR(flush_log_at_trx_commit),
   MYSQL_SYSVAR(flush_method),

storage/innobase/include/srv0srv.h

@@ -89,6 +89,8 @@ extern ulint	srv_awe_window_size;
 extern ulint	srv_mem_pool_size;
 extern ulint	srv_lock_table_size;
 
+extern ibool    srv_thread_concurrency_timer_based;
+
 extern ulint	srv_n_file_io_threads;
 /* Number of background IO threads for read and write. Replaces
  * srv_n_file_io_threads. */

storage/innobase/srv/srv0srv.c

@@ -171,6 +171,7 @@ ulint	srv_awe_window_size	= 0;		/* size in pages; MySQL inits
 ulint	srv_mem_pool_size	= ULINT_MAX;	/* size in bytes */
 ulint	srv_lock_table_size	= ULINT_MAX;
 
+
 ulint   srv_io_capacity         = ULINT_MAX;    /* Number of IO operations per
                                                    second the server can do */
 
@@ -288,6 +289,7 @@ Value 10 should be good if there are less than 4 processors + 4 disks in the
 computer. Bigger computers need bigger values. Value 0 will disable the
 concurrency check. */
 
+ibool   srv_thread_concurrency_timer_based = TRUE;
 ulong	srv_thread_concurrency	= 0;
 ulong	srv_commit_concurrency	= 0;
 
@@ -1061,6 +1063,91 @@ ulong	srv_max_purge_lag		= 0;
 Puts an OS thread to wait if there are too many concurrent threads
 (>= srv_thread_concurrency) inside InnoDB. The threads wait in a FIFO queue. */
 
+static void
+inc_srv_conc_n_threads(lint *n_threads)
+{
+  *n_threads = os_atomic_increment(&srv_conc_n_threads, 1);
+}
+
+static void
+dec_srv_conc_n_threads()
+{
+  os_atomic_increment(&srv_conc_n_threads, -1);
+}
+
+static void
+print_already_in_error(trx_t* trx)
+{
+	ut_print_timestamp(stderr);
+	fputs("  InnoDB: Error: trying to declare trx"
+	      " to enter InnoDB, but\n"
+	      "InnoDB: it already is declared.\n", stderr);
+	trx_print(stderr, trx, 0);
+	putc('\n', stderr);
+        return;
+}
+
+static void
+enter_innodb_with_tickets(trx_t* trx)
+{
+	trx->declared_to_be_inside_innodb = TRUE;
+	trx->n_tickets_to_enter_innodb = SRV_FREE_TICKETS_TO_ENTER;
+        return;
+}
+
+static void
+srv_conc_enter_innodb_timer_based(trx_t* trx)
+{
+        lint               conc_n_threads;
+        ibool              has_yielded = FALSE;
+        ulint              has_slept = 0;
+
+	if (trx->declared_to_be_inside_innodb) {
+                print_already_in_error(trx);
+        }
+retry:
+	if (srv_conc_n_threads < (lint) srv_thread_concurrency) {
+                inc_srv_conc_n_threads(&conc_n_threads);
+	        if (conc_n_threads <= srv_thread_concurrency) {
+                       enter_innodb_with_tickets(trx);
+                       return;
+                }
+                dec_srv_conc_n_threads(&conc_n_threads);
+       }
+       if (!has_yielded)
+       {
+               has_yielded = TRUE;
+               os_thread_yield();
+               goto retry;
+       }
+       if (trx->has_search_latch
+           || NULL != UT_LIST_GET_FIRST(trx->trx_locks)) {
+
+                inc_srv_conc_n_threads(&conc_n_threads);
+                enter_innodb_with_tickets(trx);
+                return;
+       }
+       if (has_slept < 2)
+       {
+               trx->op_info = "sleeping before entering InnoDB";
+               os_thread_sleep(10000);
+               trx->op_info = "";
+               has_slept++;
+       }
+       inc_srv_conc_n_threads(&conc_n_threads);
+       enter_innodb_with_tickets(trx);
+       return;
+}
+
+static void
+srv_conc_exit_innodb_timer_based(trx_t* trx)
+{
+        dec_srv_conc_n_threads();
+	trx->declared_to_be_inside_innodb = FALSE;
+	trx->n_tickets_to_enter_innodb = 0;
+        return;
+}
+
 void
 srv_conc_enter_innodb(
 /*==================*/
@@ -1091,15 +1178,17 @@ srv_conc_enter_innodb(
 		return;
 	}
 
+#ifdef UNIV_SYNC_ATOMIC
+        if (srv_thread_concurrency_timer_based) {
+          srv_conc_enter_innodb_timer_based(trx);
+          return;
+        }
+#endif
+
 	os_fast_mutex_lock(&srv_conc_mutex);
 retry:
 	if (trx->declared_to_be_inside_innodb) {
-		ut_print_timestamp(stderr);
-		fputs("  InnoDB: Error: trying to declare trx"
-		      " to enter InnoDB, but\n"
-		      "InnoDB: it already is declared.\n", stderr);
-		trx_print(stderr, trx, 0);
-		putc('\n', stderr);
+                print_already_in_error(trx);
 		os_fast_mutex_unlock(&srv_conc_mutex);
 
 		return;
@@ -1226,17 +1315,25 @@ srv_conc_force_enter_innodb(
 	trx_t*	trx)	/* in: transaction object associated with the
 			thread */
 {
+        lint               conc_n_threads;
+
 	if (UNIV_LIKELY(!srv_thread_concurrency)) {
 
 		return;
 	}
 
+#ifdef UNIV_SYNC_ATOMIC
+        if (srv_thread_concurrency_timer_based) {
+                inc_srv_conc_n_threads(&conc_n_threads);
+	        trx->declared_to_be_inside_innodb = TRUE;
+	        trx->n_tickets_to_enter_innodb = 1;
+                return;
+        }
+#endif
 	os_fast_mutex_lock(&srv_conc_mutex);
-
 	srv_conc_n_threads++;
 	trx->declared_to_be_inside_innodb = TRUE;
 	trx->n_tickets_to_enter_innodb = 1;
-
 	os_fast_mutex_unlock(&srv_conc_mutex);
 }
 
@@ -1268,6 +1365,14 @@ srv_conc_force_exit_innodb(
 		return;
 	}
 
+#ifdef UNIV_SYNC_ATOMIC
+        if (srv_thread_concurrency_timer_based)
+        {
+                srv_conc_exit_innodb_timer_based(trx);
+                return;
+        }
+#endif
+
 	os_fast_mutex_lock(&srv_conc_mutex);
 
 	srv_conc_n_threads--;