From bf2924b0fc61d2e83250bc67dcc0b2d2fd66c124 Mon Sep 17 00:00:00 2001
From: Alexey Kopytov <akopytov@gmail.com>
Date: Sun, 16 Oct 2016 23:09:51 +0300
Subject: [PATCH] Use an atomic fetch-and-add instead of a global mutex in
 sb_lua_get_request().

This was a scalability bottleneck with --max-requests>0.
---
 sysbench/scripting/script_lua.c     | 18 +++++++-----------
 tests/include/script_oltp_common.sh |  2 +-
 2 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/sysbench/scripting/script_lua.c b/sysbench/scripting/script_lua.c
index 5590d7f..71f2a8a 100644
--- a/sysbench/scripting/script_lua.c
+++ b/sysbench/scripting/script_lua.c
@@ -20,6 +20,8 @@
 # include "config.h"
 #endif
 
+#include <stdlib.h>
+
 #include "script_lua.h"
 #include "lua.h"
 #include "lualib.h"
@@ -29,7 +31,7 @@
 #include "db_driver.h"
 #include "sb_rnd.h"
 
-#include <stdlib.h>
+#include "ck_pr.h"
 
 #define EVENT_FUNC "event"
 #define PREPARE_FUNC "prepare"
@@ -245,17 +247,11 @@ sb_request_t sb_lua_get_request(int thread_id)
 
   (void) thread_id; /* unused */
 
-  if (sb_globals.max_requests > 0)
+  if (sb_globals.max_requests > 0 &&
+      ck_pr_faa_uint(&nevents, 1) >= sb_globals.max_requests)
   {
-    SB_THREAD_MUTEX_LOCK();
-    if (nevents >= sb_globals.max_requests)
-    {
-      req.type = SB_REQ_TYPE_NULL;
-      SB_THREAD_MUTEX_UNLOCK();
-      return req;
-    }
-    nevents++;
-    SB_THREAD_MUTEX_UNLOCK();
+    req.type = SB_REQ_TYPE_NULL;
+    return req;
   }
 
   req.type = SB_REQ_TYPE_SCRIPT;
diff --git a/tests/include/script_oltp_common.sh b/tests/include/script_oltp_common.sh
index aa9b715..f0cacf8 100644
--- a/tests/include/script_oltp_common.sh
+++ b/tests/include/script_oltp_common.sh
@@ -12,6 +12,6 @@ ARGS="--test=${SBTEST_SCRIPTDIR}/oltp.lua $DB_DRIVER_ARGS --oltp-tables-count=8"
 
 sysbench $ARGS prepare
 
-sysbench $ARGS --max-requests=100 --num-threads=1 run
+sysbench $ARGS --max-requests=100 --num-threads=2 run
 
 sysbench $ARGS cleanup