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authorDavidlohr Bueso <dave@stgolabs.net>2014-09-11 20:40:17 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-09-16 13:39:13 -0700
commitcdf26bb10bcb50161d452b16eb3cf2901645d625 (patch)
treeba7e69bb55b3836ae06c8bb82bf9aae72a376bc5 /Documentation/locking
parent23a8e5c2d2a481fcf382490369c27b405a650212 (diff)
downloadlinux-cdf26bb10bcb50161d452b16eb3cf2901645d625.tar.bz2
locktorture: Add documentation
Just like Documentation/RCU/torture.txt, begin a document for the locktorture module. This module is still pretty green, so I have just added some specific sections to the doc (general desc, params, usage, etc.). Further development should update the file. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> [ paulmck: Apply Randy Dunlap review comments. ] Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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+Kernel Lock Torture Test Operation
+
+CONFIG_LOCK_TORTURE_TEST
+
+The CONFIG LOCK_TORTURE_TEST config option provides a kernel module
+that runs torture tests on core kernel locking primitives. The kernel
+module, 'locktorture', may be built after the fact on the running
+kernel to be tested, if desired. The tests periodically output status
+messages via printk(), which can be examined via the dmesg (perhaps
+grepping for "torture"). The test is started when the module is loaded,
+and stops when the module is unloaded. This program is based on how RCU
+is tortured, via rcutorture.
+
+This torture test consists of creating a number of kernel threads which
+acquire the lock and hold it for specific amount of time, thus simulating
+different critical region behaviors. The amount of contention on the lock
+can be simulated by either enlarging this critical region hold time and/or
+creating more kthreads.
+
+
+MODULE PARAMETERS
+
+This module has the following parameters:
+
+
+ ** Locktorture-specific **
+
+nwriters_stress Number of kernel threads that will stress exclusive lock
+ ownership (writers). The default value is twice the number
+ of online CPUs.
+
+torture_type Type of lock to torture. By default, only spinlocks will
+ be tortured. This module can torture the following locks,
+ with string values as follows:
+
+ o "lock_busted": Simulates a buggy lock implementation.
+
+ o "spin_lock": spin_lock() and spin_unlock() pairs.
+
+ o "spin_lock_irq": spin_lock_irq() and spin_unlock_irq()
+ pairs.
+
+torture_runnable Start locktorture at boot time in the case where the
+ module is built into the kernel, otherwise wait for
+ torture_runnable to be set via sysfs before starting.
+ By default it will begin once the module is loaded.
+
+
+ ** Torture-framework (RCU + locking) **
+
+shutdown_secs The number of seconds to run the test before terminating
+ the test and powering off the system. The default is
+ zero, which disables test termination and system shutdown.
+ This capability is useful for automated testing.
+
+onoff_interval The number of seconds between each attempt to execute a
+ randomly selected CPU-hotplug operation. Defaults
+ to zero, which disables CPU hotplugging. In
+ CONFIG_HOTPLUG_CPU=n kernels, locktorture will silently
+ refuse to do any CPU-hotplug operations regardless of
+ what value is specified for onoff_interval.
+
+onoff_holdoff The number of seconds to wait until starting CPU-hotplug
+ operations. This would normally only be used when
+ locktorture was built into the kernel and started
+ automatically at boot time, in which case it is useful
+ in order to avoid confusing boot-time code with CPUs
+ coming and going. This parameter is only useful if
+ CONFIG_HOTPLUG_CPU is enabled.
+
+stat_interval Number of seconds between statistics-related printk()s.
+ By default, locktorture will report stats every 60 seconds.
+ Setting the interval to zero causes the statistics to
+ be printed -only- when the module is unloaded, and this
+ is the default.
+
+stutter The length of time to run the test before pausing for this
+ same period of time. Defaults to "stutter=5", so as
+ to run and pause for (roughly) five-second intervals.
+ Specifying "stutter=0" causes the test to run continuously
+ without pausing, which is the old default behavior.
+
+shuffle_interval The number of seconds to keep the test threads affinitied
+ to a particular subset of the CPUs, defaults to 3 seconds.
+ Used in conjunction with test_no_idle_hz.
+
+verbose Enable verbose debugging printing, via printk(). Enabled
+ by default. This extra information is mostly related to
+ high-level errors and reports from the main 'torture'
+ framework.
+
+
+STATISTICS
+
+Statistics are printed in the following format:
+
+spin_lock-torture: Writes: Total: 93746064 Max/Min: 0/0 Fail: 0
+ (A) (B) (C) (D)
+
+(A): Lock type that is being tortured -- torture_type parameter.
+
+(B): Number of times the lock was acquired.
+
+(C): Min and max number of times threads failed to acquire the lock.
+
+(D): true/false values if there were errors acquiring the lock. This should
+ -only- be positive if there is a bug in the locking primitive's
+ implementation. Otherwise a lock should never fail (i.e., spin_lock()).
+ Of course, the same applies for (C), above. A dummy example of this is
+ the "lock_busted" type.
+
+USAGE
+
+The following script may be used to torture locks:
+
+ #!/bin/sh
+
+ modprobe locktorture
+ sleep 3600
+ rmmod locktorture
+ dmesg | grep torture:
+
+The output can be manually inspected for the error flag of "!!!".
+One could of course create a more elaborate script that automatically
+checked for such errors. The "rmmod" command forces a "SUCCESS",
+"FAILURE", or "RCU_HOTPLUG" indication to be printk()ed. The first
+two are self-explanatory, while the last indicates that while there
+were no locking failures, CPU-hotplug problems were detected.
+
+Also see: Documentation/RCU/torture.txt