The attached patch adds a module for testing and benchmarking mutexes,

semaphores and R/W semaphores.

Using it is simple:

	insmod synchro-test.ko <args>

It will exit with error ENOANO after running the tests and printing the
results to the kernel console log.

The available arguments are:

 (*) mx=N

	Start up to N mutex thrashing threads, where N is at most 20. All will
	try and thrash the same mutex.

 (*) sm=N

	Start up to N counting semaphore thrashing threads, where N is at most
	20. All will try and thrash the same semaphore.

 (*) ism=M

	Initialise the counting semaphore with M, where M is any positive
	integer greater than zero. The default is 4.

 (*) rd=N
 (*) wr=O
 (*) dg=P

	Start up to N reader thrashing threads, O writer thrashing threads and
	P downgrader thrashing threads, where N, O and P are at most 20
	apiece. All will try and thrash the same read/write semaphore.

 (*) elapse=N

	Run the tests for N seconds. The default is 5.

 (*) load=N

	Each thread delays for N uS whilst holding the lock. The dfault is 0.

 (*) interval=N

	Each thread delays for N uS whilst not holding the lock. The default
	is 0.

 (*) do_sched=1

	Each thread will call schedule if required after each iteration.

 (*) v=1

	Print more verbose information, including a thread iteration
	distribution list.

The module should be enabled by turning on CONFIG_DEBUG_SYNCHRO_TEST to "m".
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/synchro-test.txt

+The synchro-test.ko module can be used for testing and benchmarking mutexes,
+semaphores and R/W semaphores.
+
+The module is compiled by setting CONFIG_DEBUG_SYNCHRO_TEST to "m" when
+configuring the kernel.
+
+Using it is simple:
+
+	insmod synchro-test.ko <args>
+
+It will exit with error ENOANO after running the tests and printing the
+results to the kernel console log.
+
+The available arguments are:
+
+ (*) mx=N
+
+	Start up to N mutex thrashing threads, where N is at most 20. All will
+	try and thrash the same mutex.
+
+ (*) sm=N
+
+	Start up to N counting semaphore thrashing threads, where N is at most
+	20. All will try and thrash the same semaphore.
+
+ (*) ism=M
+
+	Initialise the counting semaphore with M, where M is any positive
+	integer greater than zero. The default is 4.
+
+ (*) rd=N
+ (*) wr=O
+ (*) dg=P
+
+	Start up to N reader thrashing threads, O writer thrashing threads and
+	P downgrader thrashing threads, where N, O and P are at most 20
+	apiece. All will try and thrash the same read/write semaphore.
+
+ (*) elapse=N
+
+	Run the tests for N seconds. The default is 5.
+
+ (*) load=N
+
+	Each thread delays for N uS whilst holding the lock. The default is 0.
+
+ (*) interval=N
+
+	Each thread delays for N uS whilst not holding the lock. The default
+	is 0.
+
+ (*) do_sched=1
+
+	Each thread will call schedule if required after each iteration.
+
+ (*) v=1
+
+	Print more verbose information, including a thread iteration
+	distribution list.

kernel/Makefile

@@ -64,6 +64,7 @@ obj-$(CONFIG_CGROUP_NS) += ns_cgroup.o
 obj-$(CONFIG_UTS_NS) += utsname.o
 obj-$(CONFIG_USER_NS) += user_namespace.o
 obj-$(CONFIG_PID_NS) += pid_namespace.o
+obj-$(CONFIG_DEBUG_SYNCHRO_TEST) += synchro-test.o
 obj-$(CONFIG_IKCONFIG) += configs.o
 obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o
 obj-$(CONFIG_STOP_MACHINE) += stop_machine.o

lib/Kconfig.debug

@@ -719,6 +719,20 @@ config FRAME_POINTER
 	  larger and slower, but it gives very useful debugging information
 	  in case of kernel bugs. (precise oopses/stacktraces/warnings)
 
+config DEBUG_SYNCHRO_TEST
+	tristate "Synchronisation primitive testing module"
+	depends on DEBUG_KERNEL
+	default n
+	help
+	  This option provides a kernel module that can thrash the sleepable
+	  synchronisation primitives (mutexes and semaphores).
+
+	  You should say N or M here. Whilst the module can be built in, it's
+	  not recommended as it requires module parameters supplying to get it
+	  to do anything.
+
+	  See Documentation/synchro-test.txt.
+
 config BOOT_PRINTK_DELAY
 	bool "Delay each boot printk message by N milliseconds"
 	depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY