Merge lp:~laurynas-biveinis/percona-server/xtradb-thread-priority-flag into lp:percona-server/5.6

[Laurynas Biveinis]

Implement thread priority flag
(https://blueprints.launchpad.net/percona-server/+spec/xtradb-thread-priority-flag)
that would be available for InnoDB threads to check whether they
should acquire some shared resource with priority or no. The actual
uses of this flag will be in follow-up.

This flag srv_current_thread_priority is implemented through
thread-local storage. There were two other alternatives considered
for its implementation.
1. Passing the flag value from the DECLARE_THREAD functions to its use
   sites through the callstacks. But such callstacks would be very
   deep and would require patching dozens of InnoDB functions to
   include this new arg.
2. pthread_setspecific()/pthread_getspecific(). This would have the
   advantage of being slightly more portable than TLS, but it's more
   complicated to use: 1) the flag would have to be allocated in
   heap. 2) pthread_key_create() calls through pthread_once() would
   be necessary, moreover they'd have to be placed in mysys instead of
   InnoDB and any affected non-mysys-initializing threads in InnoDB
   would have to be converted to initialize mysys. 3)
   pthread_getspecific() calls would have to happen in very hot code
   paths, such as mutex locking/unlocking code.

Thus TLS appears to be the best option.

Means to change the flag value for individual InnoDB utility threads
are provided for UNIV_PERF_DEBUG or UNIV_DEBUG builds through the new
global dynamic variables innodb_priority_purge, innodb_priority_io,
innodb_priority_cleaner, innodb_priority_master. Added sys_vars tests
for them.

http://jenkins.percona.com/job/percona-server-5.6-param/281/

[Alexey Kopytov (akopytov)]

Just make it Linux-specific for now, i.e. so that the system variables only appear in UNIV_LINUX builds, and srv_current_thread_priority is #define'd to 0 otherwise.

Making it truly portable is more complex than just #ifdef __GNUC__, and I will address it later.

But I also don't like reviewing this change in isolation. Please resubmit with the code that actually makes use of srv_current_thread_priority.

review: Needs Resubmitting

[Laurynas Biveinis (laurynas-biveinis)]

Yes, UNIV_LINUX makes more sense than __GNUC__.

Re. isolation. The whole set of changes would be as follows, in the smallest parts:
- This MP.
- Priority mutex implementation.
- Specific buffer pool free list mutex conversion to priority.
- Non-specific mutex conversion to priority: dict_sys, LRU list, rseg, log.
- Priority rwlatch implementation.
- Non-specific rwlatch conversion to priority: fsp, page_hash, AHI, index, purge.

How this should be distributed among MPs? One big one with everything? Are separate commits OK or one big commit too?

Thanks.

[Alexey Kopytov (akopytov)]

1 MP, multiple commits should be fine.

=== added file 'Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_cleaner_basic.result'
--- Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_cleaner_basic.result	1970-01-01 00:00:00 +0000
+++ Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_cleaner_basic.result	2013-09-20 12:09:05 +0000
@@ -0,0 +1,31 @@
+SET @start_value = @@GLOBAL.innodb_priority_cleaner;
+SELECT @@GLOBAL.innodb_priority_cleaner;
+@@GLOBAL.innodb_priority_cleaner
+0
+SELECT @@SESSION.innodb_priority_cleaner;
+ERROR HY000: Variable 'innodb_priority_cleaner' is a GLOBAL variable
+SET GLOBAL innodb_priority_cleaner='OFF';
+SELECT @@GLOBAL.innodb_priority_cleaner;
+@@GLOBAL.innodb_priority_cleaner
+0
+SET GLOBAL innodb_priority_cleaner='ON';
+SELECT @@GLOBAL.innodb_priority_cleaner;
+@@GLOBAL.innodb_priority_cleaner
+1
+SET GLOBAL innodb_priority_cleaner=0;
+SELECT @@GLOBAL.innodb_priority_cleaner;
+@@GLOBAL.innodb_priority_cleaner
+0
+SET GLOBAL innodb_priority_cleaner=1;
+SELECT @@GLOBAL.innodb_priority_cleaner;
+@@GLOBAL.innodb_priority_cleaner
+1
+SET GLOBAL innodb_priority_cleaner=1.1;
+ERROR 42000: Incorrect argument type to variable 'innodb_priority_cleaner'
+SET GLOBAL innodb_priority_cleaner=1e1;
+ERROR 42000: Incorrect argument type to variable 'innodb_priority_cleaner'
+SET GLOBAL innodb_priority_cleaner=2;
+ERROR 42000: Variable 'innodb_priority_cleaner' can't be set to the value of '2'
+SET GLOBAL innodb_priority_cleaner='foo';
+ERROR 42000: Variable 'innodb_priority_cleaner' can't be set to the value of 'foo'
+SET GLOBAL innodb_priority_cleaner = @start_value;

=== added file 'Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_io_basic.result'
--- Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_io_basic.result	1970-01-01 00:00:00 +0000
+++ Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_io_basic.result	2013-09-20 12:09:05 +0000
@@ -0,0 +1,31 @@
+SET @start_value = @@GLOBAL.innodb_priority_io;
+SELECT @@GLOBAL.innodb_priority_io;
+@@GLOBAL.innodb_priority_io
+0
+SELECT @@SESSION.innodb_priority_io;
+ERROR HY000: Variable 'innodb_priority_io' is a GLOBAL variable
+SET GLOBAL innodb_priority_io='OFF';
+SELECT @@GLOBAL.innodb_priority_io;
+@@GLOBAL.innodb_priority_io
+0
+SET GLOBAL innodb_priority_io='ON';
+SELECT @@GLOBAL.innodb_priority_io;
+@@GLOBAL.innodb_priority_io
+1
+SET GLOBAL innodb_priority_io=0;
+SELECT @@GLOBAL.innodb_priority_io;
+@@GLOBAL.innodb_priority_io
+0
+SET GLOBAL innodb_priority_io=1;
+SELECT @@GLOBAL.innodb_priority_io;
+@@GLOBAL.innodb_priority_io
+1
+SET GLOBAL innodb_priority_io=1.1;
+ERROR 42000: Incorrect argument type to variable 'innodb_priority_io'
+SET GLOBAL innodb_priority_io=1e1;
+ERROR 42000: Incorrect argument type to variable 'innodb_priority_io'
+SET GLOBAL innodb_priority_io=2;
+ERROR 42000: Variable 'innodb_priority_io' can't be set to the value of '2'
+SET GLOBAL innodb_priority_io='foo';
+ERROR 42000: Variable 'innodb_priority_io' can't be set to the value of 'foo'
+SET GLOBAL innodb_priority_io = @start_value;

=== added file 'Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_master_basic.result'
--- Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_master_basic.result	1970-01-01 00:00:00 +0000
+++ Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_master_basic.result	2013-09-20 12:09:05 +0000
@@ -0,0 +1,31 @@
+SET @start_value = @@GLOBAL.innodb_priority_master;
+SELECT @@GLOBAL.innodb_priority_master;
+@@GLOBAL.innodb_priority_master
+0
+SELECT @@SESSION.innodb_priority_master;
+ERROR HY000: Variable 'innodb_priority_master' is a GLOBAL variable
+SET GLOBAL innodb_priority_master='OFF';
+SELECT @@GLOBAL.innodb_priority_master;
+@@GLOBAL.innodb_priority_master
+0
+SET GLOBAL innodb_priority_master='ON';
+SELECT @@GLOBAL.innodb_priority_master;
+@@GLOBAL.innodb_priority_master
+1
+SET GLOBAL innodb_priority_master=0;
+SELECT @@GLOBAL.innodb_priority_master;
+@@GLOBAL.innodb_priority_master
+0
+SET GLOBAL innodb_priority_master=1;
+SELECT @@GLOBAL.innodb_priority_master;
+@@GLOBAL.innodb_priority_master
+1
+SET GLOBAL innodb_priority_master=1.1;
+ERROR 42000: Incorrect argument type to variable 'innodb_priority_master'
+SET GLOBAL innodb_priority_master=1e1;
+ERROR 42000: Incorrect argument type to variable 'innodb_priority_master'
+SET GLOBAL innodb_priority_master=2;
+ERROR 42000: Variable 'innodb_priority_master' can't be set to the value of '2'
+SET GLOBAL innodb_priority_master='foo';
+ERROR 42000: Variable 'innodb_priority_master' can't be set to the value of 'foo'
+SET GLOBAL innodb_priority_master = @start_value;

=== added file 'Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_purge_basic.result'
--- Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_purge_basic.result	1970-01-01 00:00:00 +0000
+++ Percona-Server/mysql-test/suite/sys_vars/r/innodb_priority_purge_basic.result	2013-09-20 12:09:05 +0000
@@ -0,0 +1,31 @@
+SET @start_value = @@GLOBAL.innodb_priority_purge;
+SELECT @@GLOBAL.innodb_priority_purge;
+@@GLOBAL.innodb_priority_purge
+0
+SELECT @@SESSION.innodb_priority_purge;
+ERROR HY000: Variable 'innodb_priority_purge' is a GLOBAL variable
+SET GLOBAL innodb_priority_purge='OFF';
+SELECT @@GLOBAL.innodb_priority_purge;
+@@GLOBAL.innodb_priority_purge
+0
+SET GLOBAL innodb_priority_purge='ON';
+SELECT @@GLOBAL.innodb_priority_purge;
+@@GLOBAL.innodb_priority_purge
+1
+SET GLOBAL innodb_priority_purge=0;
+SELECT @@GLOBAL.innodb_priority_purge;
+@@GLOBAL.innodb_priority_purge
+0
+SET GLOBAL innodb_priority_purge=1;
+SELECT @@GLOBAL.innodb_priority_purge;
+@@GLOBAL.innodb_priority_purge
+1
+SET GLOBAL innodb_priority_purge=1.1;
+ERROR 42000: Incorrect argument type to variable 'innodb_priority_purge'
+SET GLOBAL innodb_priority_purge=1e1;
+ERROR 42000: Incorrect argument type to variable 'innodb_priority_purge'
+SET GLOBAL innodb_priority_purge=2;
+ERROR 42000: Variable 'innodb_priority_purge' can't be set to the value of '2'
+SET GLOBAL innodb_priority_purge='foo';
+ERROR 42000: Variable 'innodb_priority_purge' can't be set to the value of 'foo'
+SET GLOBAL innodb_priority_purge = @start_value;

=== added file 'Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_cleaner_basic.test'
--- Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_cleaner_basic.test	1970-01-01 00:00:00 +0000
+++ Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_cleaner_basic.test	2013-09-20 12:09:05 +0000
@@ -0,0 +1,35 @@
+--source include/have_debug.inc
+--source include/have_innodb.inc
+
+# A dynamic, global variable
+
+SET @start_value = @@GLOBAL.innodb_priority_cleaner;
+
+# Default value
+SELECT @@GLOBAL.innodb_priority_cleaner;
+
+# Global only
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+SELECT @@SESSION.innodb_priority_cleaner;
+
+# Correct values
+SET GLOBAL innodb_priority_cleaner='OFF';
+SELECT @@GLOBAL.innodb_priority_cleaner;
+SET GLOBAL innodb_priority_cleaner='ON';
+SELECT @@GLOBAL.innodb_priority_cleaner;
+SET GLOBAL innodb_priority_cleaner=0;
+SELECT @@GLOBAL.innodb_priority_cleaner;
+SET GLOBAL innodb_priority_cleaner=1;
+SELECT @@GLOBAL.innodb_priority_cleaner;
+
+# Incorrect values
+--error ER_WRONG_TYPE_FOR_VAR
+SET GLOBAL innodb_priority_cleaner=1.1;
+--error ER_WRONG_TYPE_FOR_VAR
+SET GLOBAL innodb_priority_cleaner=1e1;
+--error ER_WRONG_VALUE_FOR_VAR
+SET GLOBAL innodb_priority_cleaner=2;
+--error ER_WRONG_VALUE_FOR_VAR
+SET GLOBAL innodb_priority_cleaner='foo';
+
+SET GLOBAL innodb_priority_cleaner = @start_value;

=== added file 'Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_io_basic.test'
--- Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_io_basic.test	1970-01-01 00:00:00 +0000
+++ Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_io_basic.test	2013-09-20 12:09:05 +0000
@@ -0,0 +1,35 @@
+--source include/have_debug.inc
+--source include/have_innodb.inc
+
+# A dynamic, global variable
+
+SET @start_value = @@GLOBAL.innodb_priority_io;
+
+# Default value
+SELECT @@GLOBAL.innodb_priority_io;
+
+# Global only
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+SELECT @@SESSION.innodb_priority_io;
+
+# Correct values
+SET GLOBAL innodb_priority_io='OFF';
+SELECT @@GLOBAL.innodb_priority_io;
+SET GLOBAL innodb_priority_io='ON';
+SELECT @@GLOBAL.innodb_priority_io;
+SET GLOBAL innodb_priority_io=0;
+SELECT @@GLOBAL.innodb_priority_io;
+SET GLOBAL innodb_priority_io=1;
+SELECT @@GLOBAL.innodb_priority_io;
+
+# Incorrect values
+--error ER_WRONG_TYPE_FOR_VAR
+SET GLOBAL innodb_priority_io=1.1;
+--error ER_WRONG_TYPE_FOR_VAR
+SET GLOBAL innodb_priority_io=1e1;
+--error ER_WRONG_VALUE_FOR_VAR
+SET GLOBAL innodb_priority_io=2;
+--error ER_WRONG_VALUE_FOR_VAR
+SET GLOBAL innodb_priority_io='foo';
+
+SET GLOBAL innodb_priority_io = @start_value;

=== added file 'Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_master_basic.test'
--- Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_master_basic.test	1970-01-01 00:00:00 +0000
+++ Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_master_basic.test	2013-09-20 12:09:05 +0000
@@ -0,0 +1,35 @@
+--source include/have_debug.inc
+--source include/have_innodb.inc
+
+# A dynamic, global variable
+
+SET @start_value = @@GLOBAL.innodb_priority_master;
+
+# Default value
+SELECT @@GLOBAL.innodb_priority_master;
+
+# Global only
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+SELECT @@SESSION.innodb_priority_master;
+
+# Correct values
+SET GLOBAL innodb_priority_master='OFF';
+SELECT @@GLOBAL.innodb_priority_master;
+SET GLOBAL innodb_priority_master='ON';
+SELECT @@GLOBAL.innodb_priority_master;
+SET GLOBAL innodb_priority_master=0;
+SELECT @@GLOBAL.innodb_priority_master;
+SET GLOBAL innodb_priority_master=1;
+SELECT @@GLOBAL.innodb_priority_master;
+
+# Incorrect values
+--error ER_WRONG_TYPE_FOR_VAR
+SET GLOBAL innodb_priority_master=1.1;
+--error ER_WRONG_TYPE_FOR_VAR
+SET GLOBAL innodb_priority_master=1e1;
+--error ER_WRONG_VALUE_FOR_VAR
+SET GLOBAL innodb_priority_master=2;
+--error ER_WRONG_VALUE_FOR_VAR
+SET GLOBAL innodb_priority_master='foo';
+
+SET GLOBAL innodb_priority_master = @start_value;

=== added file 'Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_purge_basic.test'
--- Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_purge_basic.test	1970-01-01 00:00:00 +0000
+++ Percona-Server/mysql-test/suite/sys_vars/t/innodb_priority_purge_basic.test	2013-09-20 12:09:05 +0000
@@ -0,0 +1,35 @@
+--source include/have_debug.inc
+--source include/have_innodb.inc
+
+# A dynamic, global variable
+
+SET @start_value = @@GLOBAL.innodb_priority_purge;
+
+# Default value
+SELECT @@GLOBAL.innodb_priority_purge;
+
+# Global only
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+SELECT @@SESSION.innodb_priority_purge;
+
+# Correct values
+SET GLOBAL innodb_priority_purge='OFF';
+SELECT @@GLOBAL.innodb_priority_purge;
+SET GLOBAL innodb_priority_purge='ON';
+SELECT @@GLOBAL.innodb_priority_purge;
+SET GLOBAL innodb_priority_purge=0;
+SELECT @@GLOBAL.innodb_priority_purge;
+SET GLOBAL innodb_priority_purge=1;
+SELECT @@GLOBAL.innodb_priority_purge;
+
+# Incorrect values
+--error ER_WRONG_TYPE_FOR_VAR
+SET GLOBAL innodb_priority_purge=1.1;
+--error ER_WRONG_TYPE_FOR_VAR
+SET GLOBAL innodb_priority_purge=1e1;
+--error ER_WRONG_VALUE_FOR_VAR
+SET GLOBAL innodb_priority_purge=2;
+--error ER_WRONG_VALUE_FOR_VAR
+SET GLOBAL innodb_priority_purge='foo';
+
+SET GLOBAL innodb_priority_purge = @start_value;

=== modified file 'Percona-Server/storage/innobase/buf/buf0flu.cc'
--- Percona-Server/storage/innobase/buf/buf0flu.cc	2013-09-20 05:27:28 +0000
+++ Percona-Server/storage/innobase/buf/buf0flu.cc	2013-09-20 12:09:05 +0000
@@ -2441,6 +2441,8 @@
 
 	while (srv_shutdown_state == SRV_SHUTDOWN_NONE) {
 
+		srv_current_thread_priority = srv_cleaner_thread_priority;
+
 		/* The page_cleaner skips sleep if the server is
 		idle and there are no pending IOs in the buffer pool
 		and there is work to do. */

=== modified file 'Percona-Server/storage/innobase/handler/ha_innodb.cc'
--- Percona-Server/storage/innobase/handler/ha_innodb.cc	2013-09-20 05:27:28 +0000
+++ Percona-Server/storage/innobase/handler/ha_innodb.cc	2013-09-20 12:09:05 +0000
@@ -16471,6 +16471,27 @@
   PLUGIN_VAR_OPCMDARG | PLUGIN_VAR_READONLY,
   "Number of pages reserved in doublewrite buffer for batch flushing",
   NULL, NULL, 120, 1, 127, 0);
+
+static MYSQL_SYSVAR_BOOL(priority_purge, srv_purge_thread_priority,
+  PLUGIN_VAR_OPCMDARG,
+  "Make purge coordinator and worker threads acquire shared resources with "
+  "priority", NULL, NULL, FALSE);
+
+static MYSQL_SYSVAR_BOOL(priority_io, srv_io_thread_priority,
+  PLUGIN_VAR_OPCMDARG,
+  "Make I/O threads acquire shared resources with priority",
+   NULL, NULL, FALSE);
+
+static MYSQL_SYSVAR_BOOL(priority_cleaner, srv_cleaner_thread_priority,
+  PLUGIN_VAR_OPCMDARG,
+  "Make buffer pool cleaner thread acquire shared resources with priority",
+  NULL, NULL, FALSE);
+
+static MYSQL_SYSVAR_BOOL(priority_master, srv_master_thread_priority,
+  PLUGIN_VAR_OPCMDARG,
+  "Make buffer pool cleaner thread acquire shared resources with priority",
+   NULL, NULL, FALSE);
+
 #endif /* defined UNIV_DEBUG || defined UNIV_PERF_DEBUG */
 
 static MYSQL_SYSVAR_LONG(buffer_pool_instances, innobase_buffer_pool_instances,
@@ -17125,6 +17146,10 @@
 #if defined UNIV_DEBUG || defined UNIV_PERF_DEBUG
   MYSQL_SYSVAR(page_hash_locks),
   MYSQL_SYSVAR(doublewrite_batch_size),
+  MYSQL_SYSVAR(priority_purge),
+  MYSQL_SYSVAR(priority_io),
+  MYSQL_SYSVAR(priority_cleaner),
+  MYSQL_SYSVAR(priority_master),
 #endif /* defined UNIV_DEBUG || defined UNIV_PERF_DEBUG */
   MYSQL_SYSVAR(print_all_deadlocks),
   MYSQL_SYSVAR(cmp_per_index_enabled),

=== modified file 'Percona-Server/storage/innobase/include/srv0srv.h'
--- Percona-Server/storage/innobase/include/srv0srv.h	2013-08-06 15:16:34 +0000
+++ Percona-Server/storage/innobase/include/srv0srv.h	2013-09-20 12:09:05 +0000
@@ -479,6 +479,22 @@
 extern const char* srv_io_thread_op_info[];
 extern const char* srv_io_thread_function[];
 
+/* The relative priority of the current thread.  If 0, low priority; if 1, high
+priority.  */
+extern UNIV_THREAD_LOCAL ulint srv_current_thread_priority;
+
+/* The relative priority of the purge coordinator and worker threads.  */
+extern my_bool srv_purge_thread_priority;
+
+/* The relative priority of the I/O threads.  */
+extern my_bool srv_io_thread_priority;
+
+/* The relative priority of the cleaner thread.  */
+extern my_bool srv_cleaner_thread_priority;
+
+/* The relative priority of the master thread.  */
+extern my_bool srv_master_thread_priority;
+
 /* the number of purge threads to use from the worker pool (currently 0 or 1) */
 extern ulong srv_n_purge_threads;
 

=== modified file 'Percona-Server/storage/innobase/include/univ.i'
--- Percona-Server/storage/innobase/include/univ.i	2013-08-29 17:05:40 +0000
+++ Percona-Server/storage/innobase/include/univ.i	2013-09-20 12:09:05 +0000
@@ -277,6 +277,12 @@
 # define UNIV_COLD /* empty */
 #endif
 
+#if defined(__GNUC__)
+# define UNIV_THREAD_LOCAL __thread
+#else
+# error "Please define the TLS storage specifier for your platform"
+#endif
+
 #ifndef UNIV_MUST_NOT_INLINE
 /* Definition for inline version */
 

=== modified file 'Percona-Server/storage/innobase/srv/srv0srv.cc'
--- Percona-Server/storage/innobase/srv/srv0srv.cc	2013-09-02 12:24:08 +0000
+++ Percona-Server/storage/innobase/srv/srv0srv.cc	2013-09-20 12:09:05 +0000
@@ -319,6 +319,22 @@
 /* Number of iterations over which adaptive flushing is averaged. */
 UNIV_INTERN ulong	srv_flushing_avg_loops		= 30;
 
+/* The relative priority of the current thread.  If 0, low priority; if 1, high
+priority.  */
+UNIV_INTERN UNIV_THREAD_LOCAL ulint srv_current_thread_priority = 0;
+
+/* The relative priority of the purge coordinator and worker threads.  */
+UNIV_INTERN my_bool	srv_purge_thread_priority	= FALSE;
+
+/* The relative priority of the I/O threads.  */
+UNIV_INTERN my_bool	srv_io_thread_priority		= FALSE;
+
+/* The relative priority of the cleaner thread.  */
+UNIV_INTERN my_bool	srv_cleaner_thread_priority	= FALSE;
+
+/* The relative priority of the master thread.  */
+UNIV_INTERN my_bool	srv_master_thread_priority	= FALSE;
+
 /* The number of purge threads to use.*/
 UNIV_INTERN ulong	srv_n_purge_threads = 1;
 
@@ -2857,6 +2873,8 @@
 
 		MONITOR_INC(MONITOR_MASTER_THREAD_SLEEP);
 
+		srv_current_thread_priority = srv_master_thread_priority;
+
 		if (srv_check_activity(old_activity_count)) {
 			old_activity_count = srv_get_activity_count();
 			srv_master_do_active_tasks();
@@ -2997,6 +3015,8 @@
 
 		os_event_wait(slot->event);
 
+		srv_current_thread_priority = srv_purge_thread_priority;
+
 		if (srv_task_execute()) {
 
 			/* If there are tasks in the queue, wakeup
@@ -3273,6 +3293,8 @@
 
 		n_total_purged = 0;
 
+		srv_current_thread_priority = srv_purge_thread_priority;
+
 		rseg_history_len = srv_do_purge(
 			srv_n_purge_threads, &n_total_purged);
 

=== modified file 'Percona-Server/storage/innobase/srv/srv0start.cc'
--- Percona-Server/storage/innobase/srv/srv0start.cc	2013-08-14 03:57:21 +0000
+++ Percona-Server/storage/innobase/srv/srv0start.cc	2013-09-20 12:09:05 +0000
@@ -476,6 +476,7 @@
 #endif /* UNIV_PFS_THREAD */
 
 	while (srv_shutdown_state != SRV_SHUTDOWN_EXIT_THREADS) {
+		srv_current_thread_priority = srv_io_thread_priority;
 		fil_aio_wait(segment);
 	}