MDEV-14482 - Cache line contention on ut_rnd_interval()

InnoDB RNG maintains global state, causing otherwise unnecessary bus
traffic. Even worse, this is cross-mutex traffic. That is, different
mutexes suffer from contention.

Fixed delay of 4 was verified to give best throughput by OLTP update
index and read-write benchmarks on Intel Broadwell (2/20/40) and
ARM (1/46/46).

This is a backport of ce0479006523bc72ed6abb703bd1f87ff256fd8a from
MariaDB Server 10.3.

5 files changed, 20 insertions, 33 deletions

diff --git a/mysql-test/suite/sys_vars/r/innodb_spin_wait_delay_basic.result b/mysql-test/suite/sys_vars/r/innodb_spin_wait_delay_basic.result
index 88516a854fe..b76ba4933f2 100644
--- a/mysql-test/suite/sys_vars/r/innodb_spin_wait_delay_basic.result
+++ b/mysql-test/suite/sys_vars/r/innodb_spin_wait_delay_basic.result
@@ -1,28 +1,28 @@
 SET @start_global_value = @@global.innodb_spin_wait_delay;
 SELECT @start_global_value;
 @start_global_value
-6
+4
 Valid values are zero or above
 select @@global.innodb_spin_wait_delay >=0;
 @@global.innodb_spin_wait_delay >=0
 1
 select @@global.innodb_spin_wait_delay;
 @@global.innodb_spin_wait_delay
-6
+4
 select @@session.innodb_spin_wait_delay;
 ERROR HY000: Variable 'innodb_spin_wait_delay' is a GLOBAL variable
 show global variables like 'innodb_spin_wait_delay';
 Variable_name	Value
-innodb_spin_wait_delay	6
+innodb_spin_wait_delay	4
 show session variables like 'innodb_spin_wait_delay';
 Variable_name	Value
-innodb_spin_wait_delay	6
+innodb_spin_wait_delay	4
 select * from information_schema.global_variables where variable_name='innodb_spin_wait_delay';
 VARIABLE_NAME	VARIABLE_VALUE
-INNODB_SPIN_WAIT_DELAY	6
+INNODB_SPIN_WAIT_DELAY	4
 select * from information_schema.session_variables where variable_name='innodb_spin_wait_delay';
 VARIABLE_NAME	VARIABLE_VALUE
-INNODB_SPIN_WAIT_DELAY	6
+INNODB_SPIN_WAIT_DELAY	4
 set global innodb_spin_wait_delay=10;
 select @@global.innodb_spin_wait_delay;
 @@global.innodb_spin_wait_delay
@@ -38,7 +38,7 @@ ERROR HY000: Variable 'innodb_spin_wait_delay' is a GLOBAL variable and should b
 set global innodb_spin_wait_delay=DEFAULT;
 select @@global.innodb_spin_wait_delay;
 @@global.innodb_spin_wait_delay
-6
+4
 set global innodb_spin_wait_delay=0;
 select @@global.innodb_spin_wait_delay;
 @@global.innodb_spin_wait_delay
@@ -111,4 +111,4 @@ INNODB_SPIN_WAIT_DELAY	0
 SET @@global.innodb_spin_wait_delay = @start_global_value;
 SELECT @@global.innodb_spin_wait_delay;
 @@global.innodb_spin_wait_delay
-6
+4
diff --git a/mysql-test/suite/sys_vars/r/sysvars_innodb.result b/mysql-test/suite/sys_vars/r/sysvars_innodb.result
index 65d47347a15..4be85752cc7 100644
--- a/mysql-test/suite/sys_vars/r/sysvars_innodb.result
+++ b/mysql-test/suite/sys_vars/r/sysvars_innodb.result
@@ -2228,10 +2228,10 @@ READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	INNODB_SPIN_WAIT_DELAY
 SESSION_VALUE	NULL
-DEFAULT_VALUE	6
+DEFAULT_VALUE	4
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	INT UNSIGNED
-VARIABLE_COMMENT	Maximum delay between polling for a spin lock (6 by default)
+VARIABLE_COMMENT	Maximum delay between polling for a spin lock (4 by default)
 NUMERIC_MIN_VALUE	0
 NUMERIC_MAX_VALUE	6000
 NUMERIC_BLOCK_SIZE	0
diff --git a/storage/innobase/handler/ha_innodb.cc b/storage/innobase/handler/ha_innodb.cc
index 7e61a38320a..1e1583804eb 100644
--- a/storage/innobase/handler/ha_innodb.cc
+++ b/storage/innobase/handler/ha_innodb.cc
@@ -20716,8 +20716,8 @@ static MYSQL_SYSVAR_ULONG(sync_spin_loops, srv_n_spin_wait_rounds,
 
 static MYSQL_SYSVAR_UINT(spin_wait_delay, srv_spin_wait_delay,
   PLUGIN_VAR_OPCMDARG,
-  "Maximum delay between polling for a spin lock (6 by default)",
-  NULL, NULL, 6, 0, 6000, 0);
+  "Maximum delay between polling for a spin lock (4 by default)",
+  NULL, NULL, 4, 0, 6000, 0);
 
 static MYSQL_SYSVAR_ULONG(thread_concurrency, srv_thread_concurrency,
   PLUGIN_VAR_RQCMDARG,
diff --git a/storage/innobase/include/ib0mutex.h b/storage/innobase/include/ib0mutex.h
index 6c04563b97a..a7289777e00 100644
--- a/storage/innobase/include/ib0mutex.h
+++ b/storage/innobase/include/ib0mutex.h
@@ -225,7 +225,7 @@ struct TTASFutexMutex {
 				return;
 			}
 
-			ut_delay(ut_rnd_interval(max_delay));
+			ut_delay(max_delay);
 		}
 
 		for (n_waits= 0;; n_waits++) {
@@ -362,7 +362,7 @@ struct TTASMutex {
 		uint32_t n_spins = 0;
 
 		while (!try_lock()) {
-			ut_delay(ut_rnd_interval(max_delay));
+			ut_delay(max_delay);
 			if (++n_spins == max_spins) {
 				os_thread_yield();
 				max_spins+= step;
@@ -516,7 +516,7 @@ struct TTASEventMutex {
 					sync_array_wait_event(sync_arr, cell);
 				}
 			} else {
-				ut_delay(ut_rnd_interval(max_delay));
+				ut_delay(max_delay);
 			}
 		}
 
diff --git a/storage/innobase/sync/sync0rw.cc b/storage/innobase/sync/sync0rw.cc
index c9b8a1e58a5..df710a53cf6 100644
--- a/storage/innobase/sync/sync0rw.cc
+++ b/storage/innobase/sync/sync0rw.cc
@@ -298,10 +298,7 @@ lock_loop:
 	/* Spin waiting for the writer field to become free */
 	HMT_low();
 	while (i < srv_n_spin_wait_rounds && lock->lock_word <= 0) {
-		if (srv_spin_wait_delay) {
-			ut_delay(ut_rnd_interval(srv_spin_wait_delay));
-		}
-
+		ut_delay(srv_spin_wait_delay);
 		i++;
 	}
 
@@ -420,13 +417,9 @@ rw_lock_x_lock_wait_func(
 
 	ut_ad(lock->lock_word <= threshold);
 
+	HMT_low();
 	while (lock->lock_word < threshold) {
-
-
-		HMT_low();
-		if (srv_spin_wait_delay) {
-			ut_delay(ut_rnd_interval(srv_spin_wait_delay));
-		}
+		ut_delay(srv_spin_wait_delay);
 
 		if (i < srv_n_spin_wait_rounds) {
 			i++;
@@ -683,10 +676,7 @@ lock_loop:
 		while (i < srv_n_spin_wait_rounds
 		       && lock->lock_word <= X_LOCK_HALF_DECR) {
 
-			if (srv_spin_wait_delay) {
-				ut_delay(ut_rnd_interval(srv_spin_wait_delay));
-			}
-
+			ut_delay(srv_spin_wait_delay);
 			i++;
 		}
 
@@ -788,10 +778,7 @@ lock_loop:
 		while (i < srv_n_spin_wait_rounds
 		       && lock->lock_word <= X_LOCK_HALF_DECR) {
 
-			if (srv_spin_wait_delay) {
-				ut_delay(ut_rnd_interval(srv_spin_wait_delay));
-			}
-
+			ut_delay(srv_spin_wait_delay);
 			i++;
 		}