RCU/torture.txt: Remove section MODULE PARAMETERS

command (perhaps grepping for "torture").  The test is started

when the module is loaded, and stops when the module is unloaded.

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().

gp_normal	Make the fake writers use normal synchronous grace-period

		primitives.

gp_exp		Make the fake writers use expedited synchronous grace-period

		primitives.  If both gp_normal and gp_exp are set, or

		if neither gp_normal nor gp_exp are set, then randomly

		choose the primitive so that about 50% are normal and

		50% expedited.  By default, neither are set, which

		gives best overall test coverage.

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(),

			along with expedited, synchronous, and polling

			variants.

		"rcu_bh": rcu_read_lock_bh(), rcu_read_unlock_bh(), and

			call_rcu_bh(), along with expedited and synchronous

			variants.

		"rcu_busted": This tests an intentionally incorrect version

			of RCU in order to help test rcutorture itself.

		"srcu": srcu_read_lock(), srcu_read_unlock() and

			call_srcu(), along with expedited and

			synchronous variants.

		"sched": preempt_disable(), preempt_enable(), and

			call_rcu_sched(), along with expedited,

			synchronous, and polling variants.

		"tasks": voluntary context switch and call_rcu_tasks(),

			along with expedited and synchronous variants.

		Defaults to "rcu".

verbose		Enable debug printk()s.  Default is disabled.

Module parameters are prefixed by "rcutorture." in

Documentation/admin-guide/kernel-parameters.txt.

OUTPUT