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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2008-06-18 12:26:49 -0400
committerIngo Molnar <mingo@elte.hu>2008-06-19 05:22:15 -0400
commit31a72bce0bd6f3e0114009288bccbc96376eeeca (patch)
tree14a817fbe0b47511d3119360c47959d48f851140 /Documentation/RCU
parentd120f65f3aaf306c957bc4c82e510f5b0f1e9b27 (diff)
rcu: make rcutorture more vicious: reinstate boot-time testing
This patch re-institutes the ability to build rcutorture directly into the Linux kernel. The reason that this capability was removed was that this could result in your kernel being pretty much useless, as rcutorture would be running starting from early boot. This problem has been avoided by (1) making rcutorture run only three seconds of every six by default, (2) adding a CONFIG_RCU_TORTURE_TEST_RUNNABLE that permits rcutorture to be quiesced at boot time, and (3) adding a sysctl in /proc named /proc/sys/kernel/rcutorture_runnable that permits rcutorture to be quiesced and unquiesced when built into the kernel. Please note that this /proc file is -not- available when rcutorture is built as a module. Please also note that to get the earlier take-no-prisoners behavior, you must use the boot command line to set rcutorture's "stutter" parameter to zero. The rcutorture quiescing mechanism is currently quite crude: loops in each rcutorture process that poll a global variable once per tick. Suggestions for improvement are welcome. The default action will be to reduce the polling rate to a few times per second. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Suggested-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'Documentation/RCU')
-rw-r--r--Documentation/RCU/torture.txt21
1 files changed, 14 insertions, 7 deletions
diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index 02b3d14c0209..516527d4bc55 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -10,13 +10,20 @@ status messages via printk(), which can be examined via the dmesg
10command (perhaps grepping for "torture"). The test is started 10command (perhaps grepping for "torture"). The test is started
11when the module is loaded, and stops when the module is unloaded. 11when the module is loaded, and stops when the module is unloaded.
12 12
13However, actually setting this config option to "y" results in the system 13CONFIG_RCU_TORTURE_TEST_RUNNABLE
14running the test immediately upon boot, and ending only when the system 14
15is taken down. Normally, one will instead want to build the system 15It is also possible to specify CONFIG_RCU_TORTURE_TEST=y, which will
16with CONFIG_RCU_TORTURE_TEST=m and to use modprobe and rmmod to control 16result in the tests being loaded into the base kernel. In this case,
17the test, perhaps using a script similar to the one shown at the end of 17the CONFIG_RCU_TORTURE_TEST_RUNNABLE config option is used to specify
18this document. Note that you will need CONFIG_MODULE_UNLOAD in order 18whether the RCU torture tests are to be started immediately during
19to be able to end the test. 19boot or whether the /proc/sys/kernel/rcutorture_runnable file is used
20to enable them. This /proc file can be used to repeatedly pause and
21restart the tests, regardless of the initial state specified by the
22CONFIG_RCU_TORTURE_TEST_RUNNABLE config option.
23
24You will normally -not- want to start the RCU torture tests during boot
25(and thus the default is CONFIG_RCU_TORTURE_TEST_RUNNABLE=n), but doing
26this can sometimes be useful in finding boot-time bugs.
20 27
21 28
22MODULE PARAMETERS 29MODULE PARAMETERS