srv0srv.c:

  If innodb_thread_concurrency would be exceeded, let a thread sleep 10 ms before entering the FIFO queue; previously, the value was 50 ms, which Peter Z considered too long

innobase/srv/srv0srv.c

@@ -951,7 +951,13 @@ srv_conc_enter_innodb(
 
 		trx->op_info = "sleeping before joining InnoDB queue";
 
-		os_thread_sleep(50000);
+		/* Peter Zaitsev suggested that we take the sleep away
+		altogether. But the sleep may be good in pathological
+		situations of lots of thread switches. Simply put some
+		threads aside for a while to reduce the number of thread
+		switches. */
+
+		os_thread_sleep(10000);
 
 		trx->op_info = "";