Documentation/RCU/torture.rst

Source file repositories/reference/linux-study-clean/Documentation/RCU/torture.rst

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Documentation/RCU/torture.rst
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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.. SPDX-License-Identifier: GPL-2.0

==========================
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.

Module parameters are prefixed by "rcutorture." in
Documentation/admin-guide/kernel-parameters.txt.

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:

*	"rtc": The hexadecimal address of the structure currently visible
	to readers.

*	"ver": The number of times since boot that the RCU writer task
	has changed the structure visible to readers.

*	"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.  :-/

*	"rta": Number of structures allocated from the torture freelist.

*	"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".

*	"rtf": Number of frees into the torture freelist.

*	"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.

*	"rtbe": A non-zero value indicates that one of the rcu_barrier()
	family of functions is not working correctly.

Annotation

Implementation Notes