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Based on kernel version 3.9. Page generated on 2013-05-02 23:13 EST.

	RCU Torture Test Operation
	
	
	CONFIG_RCU_TORTURE_TEST
	
	The CONFIG_RCU_TORTURE_TEST config option is available for all RCU
	implementations.  It creates an rcutorture kernel module that can
	be loaded to run a torture test.  The test periodically outputs
	status messages via printk(), which can be examined via the dmesg
	command (perhaps grepping for "torture").  The test is started
	when the module is loaded, and stops when the module is unloaded.
	
	CONFIG_RCU_TORTURE_TEST_RUNNABLE
	
	It is also possible to specify CONFIG_RCU_TORTURE_TEST=y, which will
	result in the tests being loaded into the base kernel.  In this case,
	the CONFIG_RCU_TORTURE_TEST_RUNNABLE config option is used to specify
	whether the RCU torture tests are to be started immediately during
	boot or whether the /proc/sys/kernel/rcutorture_runnable file is used
	to enable them.  This /proc file can be used to repeatedly pause and
	restart the tests, regardless of the initial state specified by the
	CONFIG_RCU_TORTURE_TEST_RUNNABLE config option.
	
	You will normally -not- want to start the RCU torture tests during boot
	(and thus the default is CONFIG_RCU_TORTURE_TEST_RUNNABLE=n), but doing
	this can sometimes be useful in finding boot-time bugs.
	
	
	MODULE PARAMETERS
	
	This module has the following parameters:
	
	fqs_duration	Duration (in microseconds) of artificially induced bursts
			of force_quiescent_state() invocations.  In RCU
			implementations having force_quiescent_state(), these
			bursts help force races between forcing a given grace
			period and that grace period ending on its own.
	
	fqs_holdoff	Holdoff time (in microseconds) between consecutive calls
			to force_quiescent_state() within a burst.
	
	fqs_stutter	Wait time (in seconds) between consecutive bursts
			of calls to force_quiescent_state().
	
	irqreader	Says to invoke RCU readers from irq level.  This is currently
			done via timers.  Defaults to "1" for variants of RCU that
			permit this.  (Or, more accurately, variants of RCU that do
			-not- permit this know to ignore this variable.)
	
	n_barrier_cbs	If this is nonzero, RCU barrier testing will be conducted,
			in which case n_barrier_cbs specifies the number of
			RCU callbacks (and corresponding kthreads) to use for
			this testing.  The value cannot be negative.  If you
			specify this to be non-zero when torture_type indicates a
			synchronous RCU implementation (one for which a member of
			the synchronize_rcu() rather than the call_rcu() family is
			used -- see the documentation for torture_type below), an
			error will be reported and no testing will be carried out.
	
	nfakewriters	This is the number of RCU fake writer threads to run.  Fake
			writer threads repeatedly use the synchronous "wait for
			current readers" function of the interface selected by
			torture_type, with a delay between calls to allow for various
			different numbers of writers running in parallel.
			nfakewriters defaults to 4, which provides enough parallelism
			to trigger special cases caused by multiple writers, such as
			the synchronize_srcu() early return optimization.
	
	nreaders	This is the number of RCU reading threads supported.
			The default is twice the number of CPUs.  Why twice?
			To properly exercise RCU implementations with preemptible
			read-side critical sections.
	
	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 HOTPLUG_CPU=n
			kernels, rcutorture 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
			rcutorture 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.
	
	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.
	
	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.
	
	stall_cpu	The number of seconds that a CPU should be stalled while
			within both an rcu_read_lock() and a preempt_disable().
			This stall happens only once per rcutorture run.
			If you need multiple stalls, use modprobe and rmmod to
			repeatedly run rcutorture.  The default for stall_cpu
			is zero, which prevents rcutorture from stalling a CPU.
	
			Note that attempts to rmmod rcutorture while the stall
			is ongoing will hang, so be careful what value you
			choose for this module parameter!  In addition, too-large
			values for stall_cpu might well induce failures and
			warnings in other parts of the kernel.  You have been
			warned!
	
	stall_cpu_holdoff
			The number of seconds to wait after rcutorture starts
			before stalling a CPU.  Defaults to 10 seconds.
	
	stat_interval	The number of seconds between output of torture
			statistics (via printk()).  Regardless of the interval,
			statistics are printed when the module is unloaded.
			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.
	
	test_boost	Whether or not to test the ability of RCU to do priority
			boosting.  Defaults to "test_boost=1", which performs
			RCU priority-inversion testing only if the selected
			RCU implementation supports priority boosting.  Specifying
			"test_boost=0" never performs RCU priority-inversion
			testing.  Specifying "test_boost=2" performs RCU
			priority-inversion testing even if the selected RCU
			implementation does not support RCU priority boosting,
			which can be used to test rcutorture's ability to
			carry out RCU priority-inversion testing.
	
	test_boost_interval
			The number of seconds in an RCU priority-inversion test
			cycle.	Defaults to "test_boost_interval=7".  It is
			usually wise for this value to be relatively prime to
			the value selected for "stutter".
	
	test_boost_duration
			The number of seconds to do RCU priority-inversion testing
			within any given "test_boost_interval".  Defaults to
			"test_boost_duration=4".
	
	test_no_idle_hz	Whether or not to test the ability of RCU to operate in
			a kernel that disables the scheduling-clock interrupt to
			idle CPUs.  Boolean parameter, "1" to test, "0" otherwise.
			Defaults to omitting this test.
	
	torture_type	The type of RCU to test, with string values as follows:
	
			"rcu":  rcu_read_lock(), rcu_read_unlock() and call_rcu().
	
			"rcu_sync":  rcu_read_lock(), rcu_read_unlock(), and
				synchronize_rcu().
	
			"rcu_expedited": rcu_read_lock(), rcu_read_unlock(), and
				synchronize_rcu_expedited().
	
			"rcu_bh": rcu_read_lock_bh(), rcu_read_unlock_bh(), and
				call_rcu_bh().
	
			"rcu_bh_sync": rcu_read_lock_bh(), rcu_read_unlock_bh(),
				and synchronize_rcu_bh().
	
			"rcu_bh_expedited": rcu_read_lock_bh(), rcu_read_unlock_bh(),
				and synchronize_rcu_bh_expedited().
	
			"srcu": srcu_read_lock(), srcu_read_unlock() and
				call_srcu().
	
			"srcu_sync": srcu_read_lock(), srcu_read_unlock() and
				synchronize_srcu().
	
			"srcu_expedited": srcu_read_lock(), srcu_read_unlock() and
				synchronize_srcu_expedited().
	
			"srcu_raw": srcu_read_lock_raw(), srcu_read_unlock_raw(),
				and call_srcu().
	
			"srcu_raw_sync": srcu_read_lock_raw(), srcu_read_unlock_raw(),
				and synchronize_srcu().
	
			"sched": preempt_disable(), preempt_enable(), and
				call_rcu_sched().
	
			"sched_sync": preempt_disable(), preempt_enable(), and
				synchronize_sched().
	
			"sched_expedited": preempt_disable(), preempt_enable(), and
				synchronize_sched_expedited().
	
			Defaults to "rcu".
	
	verbose		Enable debug printk()s.  Default is disabled.
	
	
	OUTPUT
	
	The statistics output is as follows:
	
		rcu-torture:--- Start of test: nreaders=16 nfakewriters=4 stat_interval=30 verbose=0 test_no_idle_hz=1 shuffle_interval=3 stutter=5 irqreader=1 fqs_duration=0 fqs_holdoff=0 fqs_stutter=3 test_boost=1/0 test_boost_interval=7 test_boost_duration=4
		rcu-torture: rtc:           (null) ver: 155441 tfle: 0 rta: 155441 rtaf: 8884 rtf: 155440 rtmbe: 0 rtbe: 0 rtbke: 0 rtbre: 0 rtbf: 0 rtb: 0 nt: 3055767
		rcu-torture: Reader Pipe:  727860534 34213 0 0 0 0 0 0 0 0 0
		rcu-torture: Reader Batch:  727877838 17003 0 0 0 0 0 0 0 0 0
		rcu-torture: Free-Block Circulation:  155440 155440 155440 155440 155440 155440 155440 155440 155440 155440 0
		rcu-torture:--- End of test: SUCCESS: nreaders=16 nfakewriters=4 stat_interval=30 verbose=0 test_no_idle_hz=1 shuffle_interval=3 stutter=5 irqreader=1 fqs_duration=0 fqs_holdoff=0 fqs_stutter=3 test_boost=1/0 test_boost_interval=7 test_boost_duration=4
	
	The command "dmesg | grep torture:" will extract this information on
	most systems.  On more esoteric configurations, it may be necessary to
	use other commands to access the output of the printk()s used by
	the RCU torture test.  The printk()s use KERN_ALERT, so they should
	be evident.  ;-)
	
	The first and last lines show the rcutorture module parameters, and the
	last line shows either "SUCCESS" or "FAILURE", based on rcutorture's
	automatic determination as to whether RCU operated correctly.
	
	The entries are as follows:
	
	o	"rtc": The hexadecimal address of the structure currently visible
		to readers.
	
	o	"ver": The number of times since boot that the RCU writer task
		has changed the structure visible to readers.
	
	o	"tfle": If non-zero, indicates that the "torture freelist"
		containing structures to be placed into the "rtc" area is empty.
		This condition is important, since it can fool you into thinking
		that RCU is working when it is not.  :-/
	
	o	"rta": Number of structures allocated from the torture freelist.
	
	o	"rtaf": Number of allocations from the torture freelist that have
		failed due to the list being empty.  It is not unusual for this
		to be non-zero, but it is bad for it to be a large fraction of
		the value indicated by "rta".
	
	o	"rtf": Number of frees into the torture freelist.
	
	o	"rtmbe": A non-zero value indicates that rcutorture believes that
		rcu_assign_pointer() and rcu_dereference() are not working
		correctly.  This value should be zero.
	
	o	"rtbe": A non-zero value indicates that one of the rcu_barrier()
		family of functions is not working correctly.
	
	o	"rtbke": rcutorture was unable to create the real-time kthreads
		used to force RCU priority inversion.  This value should be zero.
	
	o	"rtbre": Although rcutorture successfully created the kthreads
		used to force RCU priority inversion, it was unable to set them
		to the real-time priority level of 1.  This value should be zero.
	
	o	"rtbf": The number of times that RCU priority boosting failed
		to resolve RCU priority inversion.
	
	o	"rtb": The number of times that rcutorture attempted to force
		an RCU priority inversion condition.  If you are testing RCU
		priority boosting via the "test_boost" module parameter, this
		value should be non-zero.
	
	o	"nt": The number of times rcutorture ran RCU read-side code from
		within a timer handler.  This value should be non-zero only
		if you specified the "irqreader" module parameter.
	
	o	"Reader Pipe": Histogram of "ages" of structures seen by readers.
		If any entries past the first two are non-zero, RCU is broken.
		And rcutorture prints the error flag string "!!!" to make sure
		you notice.  The age of a newly allocated structure is zero,
		it becomes one when removed from reader visibility, and is
		incremented once per grace period subsequently -- and is freed
		after passing through (RCU_TORTURE_PIPE_LEN-2) grace periods.
	
		The output displayed above was taken from a correctly working
		RCU.  If you want to see what it looks like when broken, break
		it yourself.  ;-)
	
	o	"Reader Batch": Another histogram of "ages" of structures seen
		by readers, but in terms of counter flips (or batches) rather
		than in terms of grace periods.  The legal number of non-zero
		entries is again two.  The reason for this separate view is that
		it is sometimes easier to get the third entry to show up in the
		"Reader Batch" list than in the "Reader Pipe" list.
	
	o	"Free-Block Circulation": Shows the number of torture structures
		that have reached a given point in the pipeline.  The first element
		should closely correspond to the number of structures allocated,
		the second to the number that have been removed from reader view,
		and all but the last remaining to the corresponding number of
		passes through a grace period.  The last entry should be zero,
		as it is only incremented if a torture structure's counter
		somehow gets incremented farther than it should.
	
	Different implementations of RCU can provide implementation-specific
	additional information.  For example, SRCU provides the following
	additional line:
	
		srcu-torture: per-CPU(idx=1): 0(0,1) 1(0,1) 2(0,0) 3(0,1)
	
	This line shows the per-CPU counter state.  The numbers in parentheses are
	the values of the "old" and "current" counters for the corresponding CPU.
	The "idx" value maps the "old" and "current" values to the underlying
	array, and is useful for debugging.
	
	
	USAGE
	
	The following script may be used to torture RCU:
	
		#!/bin/sh
	
		modprobe rcutorture
		sleep 3600
		rmmod rcutorture
		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 RCU failures, CPU-hotplug problems were detected.

• [ RCU ]
• 00-INDEX
• arrayRCU.txt
• checklist.txt
• listRCU.txt
• lockdep-splat.txt
• lockdep.txt
• NMI-RCU.txt
• rcu.txt
• rcubarrier.txt
• rculist_nulls.txt
• rcuref.txt
• RTFP.txt
• stallwarn.txt
• torture.txt
• trace.txt
• UP.txt
• whatisRCU.txt
•