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