Applied patch recieved from Marko:

 Make innodb_thread_concurrency 0 by default, and extend the usable
 range from 0 to 1000 (0 disables the thread throttling).

innobase/include/srv0srv.h

@@ -195,7 +195,6 @@ extern mutex_t*	kernel_mutex_temp;/* mutex protecting the server, trx structs,
 #define kernel_mutex (*kernel_mutex_temp)
 
 #define SRV_MAX_N_IO_THREADS	100
-#define SRV_CONCURRENCY_THRESHOLD	20
 				
 /* Array of English strings describing the current state of an
 i/o handler thread */

innobase/srv/srv0srv.c

@@ -258,9 +258,10 @@ threads waiting for locks are not counted into the number because otherwise
 we could get a deadlock. MySQL creates a thread for each user session, and
 semaphore contention and convoy problems can occur withput this restriction.
 Value 10 should be good if there are less than 4 processors + 4 disks in the
-computer. Bigger computers need bigger values. */
+computer. Bigger computers need bigger values. Value 0 will disable the
+concurrency check. */
 
-ulong	srv_thread_concurrency	= SRV_CONCURRENCY_THRESHOLD;
+ulong	srv_thread_concurrency	= 0;
 ulong   srv_commit_concurrency  = 0;
 
 os_fast_mutex_t	srv_conc_mutex;		/* this mutex protects srv_conc data
@@ -1141,7 +1142,7 @@ srv_conc_force_enter_innodb(
 	trx_t*	trx)	/* in: transaction object associated with the
 			thread */
 {
-	if (srv_thread_concurrency >= SRV_CONCURRENCY_THRESHOLD) {
+	if (UNIV_LIKELY(!srv_thread_concurrency)) {
 	
 		return;
 	}
@@ -1167,7 +1168,7 @@ srv_conc_force_exit_innodb(
 {
 	srv_conc_slot_t*	slot	= NULL;
 
-	if (srv_thread_concurrency >= SRV_CONCURRENCY_THRESHOLD) {
+	if (UNIV_LIKELY(!srv_thread_concurrency)) {
 	
 		return;
 	}

mysql-test/r/innodb.result

@@ -1821,15 +1821,15 @@ Variable_name	Value
 innodb_sync_spin_loops	20
 show variables like "innodb_thread_concurrency";
 Variable_name	Value
-innodb_thread_concurrency	20
-set global innodb_thread_concurrency=1000;
+innodb_thread_concurrency	0
+set global innodb_thread_concurrency=1001;
 show variables like "innodb_thread_concurrency";
 Variable_name	Value
 innodb_thread_concurrency	1000
 set global innodb_thread_concurrency=0;
 show variables like "innodb_thread_concurrency";
 Variable_name	Value
-innodb_thread_concurrency	1
+innodb_thread_concurrency	0
 set global innodb_thread_concurrency=16;
 show variables like "innodb_thread_concurrency";
 Variable_name	Value

mysql-test/t/innodb.test

@@ -1316,7 +1316,7 @@ show variables like "innodb_sync_spin_loops";
 
 # Test for innodb_thread_concurrency variable
 show variables like "innodb_thread_concurrency";
-set global innodb_thread_concurrency=1000;
+set global innodb_thread_concurrency=1001;
 show variables like "innodb_thread_concurrency";
 set global innodb_thread_concurrency=0;
 show variables like "innodb_thread_concurrency";

sql/ha_innodb.cc

@@ -338,7 +338,7 @@ innodb_srv_conc_enter_innodb(
 /*=========================*/
 	trx_t*	trx)	/* in: transaction handle */
 {
-	if (UNIV_LIKELY(srv_thread_concurrency >= SRV_CONCURRENCY_THRESHOLD)) {
+	if (UNIV_LIKELY(!srv_thread_concurrency)) {
 
 		return;
 	}
@@ -355,7 +355,7 @@ innodb_srv_conc_exit_innodb(
 /*========================*/
 	trx_t*	trx)	/* in: transaction handle */
 {
-	if (UNIV_LIKELY(srv_thread_concurrency >= SRV_CONCURRENCY_THRESHOLD)) {
+	if (UNIV_LIKELY(!srv_thread_concurrency)) {
 
 		return;
 	}

sql/mysqld.cc

@@ -5504,9 +5504,11 @@ log and this option does nothing anymore.",
    (gptr*) &srv_n_spin_wait_rounds,
    0, GET_LONG, REQUIRED_ARG, 20L, 0L, ~0L, 0, 1L, 0},
   {"innodb_thread_concurrency", OPT_INNODB_THREAD_CONCURRENCY,
-   "Helps in performance tuning in heavily concurrent environments.",
+   "Helps in performance tuning in heavily concurrent environments. "
+   "Sets the maximum number of threads allowed inside InnoDB. Value 0"
+   " will disable the thread throttling.",
    (gptr*) &srv_thread_concurrency, (gptr*) &srv_thread_concurrency,
-   0, GET_LONG, REQUIRED_ARG, 20, 1, 1000, 0, 1, 0},
+   0, GET_LONG, REQUIRED_ARG, 0, 0, 1000, 0, 1, 0},
   {"innodb_commit_concurrency", OPT_INNODB_THREAD_CONCURRENCY,
    "Helps in performance tuning in heavily concurrent environments.",
    (gptr*) &srv_commit_concurrency, (gptr*) &srv_commit_concurrency,