--- /dev/null
+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 "rcutorture"). The test is started
+when the module is loaded, and stops when the module is unloaded.
+
+However, actually setting this config option to "y" results in the system
+running the test immediately upon boot, and ending only when the system
+is taken down. Normally, one will instead want to build the system
+with CONFIG_RCU_TORTURE_TEST=m and to use modprobe and rmmod to control
+the test, perhaps using a script similar to the one shown at the end of
+this document. Note that you will need CONFIG_MODULE_UNLOAD in order
+to be able to end the test.
+
+
+MODULE PARAMETERS
+
+This module has the following parameters:
+
+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.
+
+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.
+
+verbose Enable debug printk()s. Default is disabled.
+
+
+OUTPUT
+
+The statistics output is as follows:
+
+ rcutorture: --- Start of test: nreaders=16 stat_interval=0 verbose=0
+ rcutorture: rtc: 0000000000000000 ver: 1916 tfle: 0 rta: 1916 rtaf: 0 rtf: 1915
+ rcutorture: Reader Pipe: 1466408 9747 0 0 0 0 0 0 0 0 0
+ rcutorture: Reader Batch: 1464477 11678 0 0 0 0 0 0 0 0
+ rcutorture: Free-Block Circulation: 1915 1915 1915 1915 1915 1915 1915 1915 1915 1915 0
+ rcutorture: --- End of test
+
+The command "dmesg | grep rcutorture:" 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 entries are as follows:
+
+o "ggp": The number of counter flips (or batches) since boot.
+
+o "rtc": The hexadecimal address of the structure currently visible
+ to readers.
+
+o "ver": The number of times since boot that the rcutw writer task
+ has changed the structure visible to readers.
+
+o "tfle": If non-zero, indicates that the "torture freelist"
+ containing structure 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.
+
+o "rtf": Number of frees into the torture freelist.
+
+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 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.
+
+
+USAGE
+
+The following script may be used to torture RCU:
+
+ #!/bin/sh
+
+ modprobe rcutorture
+ sleep 100
+ rmmod rcutorture
+ dmesg | grep rcutorture:
+
+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.
git://git.onelab.eu / linux-2.6.git / blobdiff