MDEV-7945 - THD::enter_stage() takes 0.48% in OLTP RO

THD::enter_stage() optimizations:
- stage backup code moved to THD::backup_stage(), saves one condition
- moved check for "new_stage" out to callers that actually need it
- remnants of enter_stage() moved to sql_class.h so it can be inlined

THD::enter_stage() overhead dropped 0.48% -> 0.07%.

PROFILING::status_change() optimizations:
- "status_arg" is now checked by QUERY_PROFILE::new_status()
- no need to check "enabled": !enabled && current is impossible
- remnants of status_change() moved to sql_profile.h so it can be inlined

PROFILING::status_change() overhead dropped 0.1% -> out of radar.

sql/lock.cc

@@ -306,8 +306,8 @@ bool mysql_lock_tables(THD *thd, MYSQL_LOCK *sql_lock, uint flags)
   PSI_stage_info org_stage;
   DBUG_ENTER("mysql_lock_tables(sql_lock)");
 
-  thd->enter_stage(&stage_system_lock, &org_stage, __func__, __FILE__,
-                   __LINE__);
+  thd->backup_stage(&org_stage);
+  THD_STAGE_INFO(thd, stage_system_lock);
   if (sql_lock->table_count && lock_external(thd, sql_lock->table,
                                              sql_lock->table_count))
     goto end;

sql/sql_class.cc

@@ -557,40 +557,11 @@ void set_thd_stage_info(void *thd_arg,
   if (thd == NULL)
     thd= current_thd;
 
-  thd->enter_stage(new_stage, old_stage, calling_func, calling_file,
-                   calling_line);
-}
-
-void THD::enter_stage(const PSI_stage_info *new_stage,
-                      PSI_stage_info *old_stage,
-                      const char *calling_func,
-                      const char *calling_file,
-                      const unsigned int calling_line)
-{
-  DBUG_PRINT("THD::enter_stage", ("%s:%d", calling_file, calling_line));
-
-  if (old_stage != NULL)
-  {
-    old_stage->m_key= m_current_stage_key;
-    old_stage->m_name= proc_info;
-  }
+  if (old_stage)
+    thd->backup_stage(old_stage);
 
-  if (new_stage != NULL)
-  {
-    const char *msg= new_stage->m_name;
-
-#if defined(ENABLED_PROFILING)
-    profiling.status_change(msg, calling_func, calling_file, calling_line);
-#endif
-
-    m_current_stage_key= new_stage->m_key;
-    proc_info= msg;
-
-#ifdef HAVE_PSI_THREAD_INTERFACE
-    MYSQL_SET_STAGE(m_current_stage_key, calling_file, calling_line);
-#endif
-  }
-  return;
+  if (new_stage)
+    thd->enter_stage(new_stage, calling_func, calling_file, calling_line);
 }
 
 void thd_enter_cond(MYSQL_THD thd, mysql_cond_t *cond, mysql_mutex_t *mutex,

sql/sql_class.h

@@ -53,7 +53,7 @@ void set_thd_stage_info(void *thd,
                         const unsigned int calling_line);
 
 #define THD_STAGE_INFO(thd, stage) \
-  (thd)->enter_stage(& stage, NULL, __func__, __FILE__, __LINE__)
+  (thd)->enter_stage(&stage, __func__, __FILE__, __LINE__)
 
 #include "my_apc.h"
 #include "rpl_gtid.h"
@@ -1989,10 +1989,28 @@ class THD :public Statement,
 
 public:
   void enter_stage(const PSI_stage_info *stage,
-                   PSI_stage_info *old_stage,
                    const char *calling_func,
                    const char *calling_file,
-                   const unsigned int calling_line);
+                   const unsigned int calling_line)
+  {
+    DBUG_PRINT("THD::enter_stage", ("%s:%d", calling_file, calling_line));
+    DBUG_ASSERT(stage);
+    m_current_stage_key= stage->m_key;
+    proc_info= stage->m_name;
+#if defined(ENABLED_PROFILING)
+    profiling.status_change(stage->m_name, calling_func, calling_file,
+                            calling_line);
+#endif
+#ifdef HAVE_PSI_THREAD_INTERFACE
+    MYSQL_SET_STAGE(m_current_stage_key, calling_file, calling_line);
+#endif
+  }
+
+  void backup_stage(PSI_stage_info *stage)
+  {
+    stage->m_key= m_current_stage_key;
+    stage->m_name= proc_info;
+  }
 
   const char *get_proc_info() const
   { return proc_info; }
@@ -2915,7 +2933,10 @@ class THD :public Statement,
     mysql_mutex_assert_owner(mutex);
     mysys_var->current_mutex = mutex;
     mysys_var->current_cond = cond;
-    enter_stage(stage, old_stage, src_function, src_file, src_line);
+    if (old_stage)
+      backup_stage(old_stage);
+    if (stage)
+      enter_stage(stage, src_function, src_file, src_line);
   }
   inline void exit_cond(const PSI_stage_info *stage,
                         const char *src_function, const char *src_file,
@@ -2931,7 +2952,8 @@ class THD :public Statement,
     mysql_mutex_lock(&mysys_var->mutex);
     mysys_var->current_mutex = 0;
     mysys_var->current_cond = 0;
-    enter_stage(stage, NULL, src_function, src_file, src_line);
+    if (stage)
+      enter_stage(stage, src_function, src_file, src_line);
     mysql_mutex_unlock(&mysys_var->mutex);
     return;
   }

sql/sql_profile.cc

@@ -302,7 +302,8 @@ void QUERY_PROFILE::new_status(const char *status_arg,
   PROF_MEASUREMENT *prof;
   DBUG_ENTER("QUERY_PROFILE::status");
 
-  DBUG_ASSERT(status_arg != NULL);
+  if (!status_arg)
+    DBUG_VOID_RETURN;
 
   if ((function_arg != NULL) && (file_arg != NULL))
     prof= new PROF_MEASUREMENT(this, status_arg, function_arg, base_name(file_arg), line_arg);
@@ -336,32 +337,6 @@ PROFILING::~PROFILING()
     delete current;
 }
 
-/**
-  A new state is given, and that signals the profiler to start a new
-  timed step for the current query's profile.
-
-  @param  status_arg  name of this step
-  @param  function_arg  calling function (usually supplied from compiler)
-  @param  function_arg  calling file (usually supplied from compiler)
-  @param  function_arg  calling line number (usually supplied from compiler)
-*/
-void PROFILING::status_change(const char *status_arg,
-                              const char *function_arg,
-                              const char *file_arg, unsigned int line_arg)
-{
-  DBUG_ENTER("PROFILING::status_change");
-
-  if (status_arg == NULL)  /* We don't know how to handle that */
-    DBUG_VOID_RETURN;
-
-  if (current == NULL)  /* This profile was already discarded. */
-    DBUG_VOID_RETURN;
-
-  if (unlikely(enabled))
-    current->new_status(status_arg, function_arg, file_arg, line_arg);
-
-  DBUG_VOID_RETURN;
-}
 
 /**
   Prepare to start processing a new query.  It is an error to do this

sql/sql_profile.h

@@ -278,7 +278,14 @@ class PROFILING
 
   void status_change(const char *status_arg,
                      const char *function_arg,
-                     const char *file_arg, unsigned int line_arg);
+                     const char *file_arg, unsigned int line_arg)
+  {
+    if (unlikely(current))
+    {
+      DBUG_ASSERT(enabled);
+      current->new_status(status_arg, function_arg, file_arg, line_arg);
+    }
+  }
 
   inline void set_thd(THD *thd_arg) { thd= thd_arg; };
 

sql/sql_show.cc

@@ -7891,8 +7891,8 @@ bool get_schema_tables_result(JOIN *join,
 
   Warnings_only_error_handler err_handler;
   thd->push_internal_handler(&err_handler);
-  thd->enter_stage(&stage_filling_schema_table, &org_stage, __func__, __FILE__,
-                   __LINE__);
+  thd->backup_stage(&org_stage);
+  THD_STAGE_INFO(thd, stage_filling_schema_table);
 
   JOIN_TAB *tab;
   for (tab= first_linear_tab(join, WITHOUT_BUSH_ROOTS, WITH_CONST_TABLES);