150 строки
6.8 KiB
Plaintext
150 строки
6.8 KiB
Plaintext
RCU Torture Test Operation
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CONFIG_RCU_TORTURE_TEST
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The CONFIG_RCU_TORTURE_TEST config option is available for all RCU
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implementations. It creates an rcutorture kernel module that can
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be loaded to run a torture test. The test periodically outputs
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status messages via printk(), which can be examined via the dmesg
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command (perhaps grepping for "torture"). The test is started
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when the module is loaded, and stops when the module is unloaded.
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Module parameters are prefixed by "rcutorture." in
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Documentation/admin-guide/kernel-parameters.txt.
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OUTPUT
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The statistics output is as follows:
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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
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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
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rcu-torture: Reader Pipe: 727860534 34213 0 0 0 0 0 0 0 0 0
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rcu-torture: Reader Batch: 727877838 17003 0 0 0 0 0 0 0 0 0
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rcu-torture: Free-Block Circulation: 155440 155440 155440 155440 155440 155440 155440 155440 155440 155440 0
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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
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The command "dmesg | grep torture:" will extract this information on
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most systems. On more esoteric configurations, it may be necessary to
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use other commands to access the output of the printk()s used by
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the RCU torture test. The printk()s use KERN_ALERT, so they should
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be evident. ;-)
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The first and last lines show the rcutorture module parameters, and the
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last line shows either "SUCCESS" or "FAILURE", based on rcutorture's
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automatic determination as to whether RCU operated correctly.
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The entries are as follows:
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o "rtc": The hexadecimal address of the structure currently visible
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to readers.
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o "ver": The number of times since boot that the RCU writer task
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has changed the structure visible to readers.
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o "tfle": If non-zero, indicates that the "torture freelist"
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containing structures to be placed into the "rtc" area is empty.
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This condition is important, since it can fool you into thinking
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that RCU is working when it is not. :-/
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o "rta": Number of structures allocated from the torture freelist.
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o "rtaf": Number of allocations from the torture freelist that have
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failed due to the list being empty. It is not unusual for this
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to be non-zero, but it is bad for it to be a large fraction of
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the value indicated by "rta".
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o "rtf": Number of frees into the torture freelist.
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o "rtmbe": A non-zero value indicates that rcutorture believes that
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rcu_assign_pointer() and rcu_dereference() are not working
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correctly. This value should be zero.
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o "rtbe": A non-zero value indicates that one of the rcu_barrier()
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family of functions is not working correctly.
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o "rtbke": rcutorture was unable to create the real-time kthreads
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used to force RCU priority inversion. This value should be zero.
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o "rtbre": Although rcutorture successfully created the kthreads
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used to force RCU priority inversion, it was unable to set them
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to the real-time priority level of 1. This value should be zero.
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o "rtbf": The number of times that RCU priority boosting failed
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to resolve RCU priority inversion.
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o "rtb": The number of times that rcutorture attempted to force
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an RCU priority inversion condition. If you are testing RCU
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priority boosting via the "test_boost" module parameter, this
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value should be non-zero.
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o "nt": The number of times rcutorture ran RCU read-side code from
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within a timer handler. This value should be non-zero only
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if you specified the "irqreader" module parameter.
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o "Reader Pipe": Histogram of "ages" of structures seen by readers.
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If any entries past the first two are non-zero, RCU is broken.
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And rcutorture prints the error flag string "!!!" to make sure
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you notice. The age of a newly allocated structure is zero,
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it becomes one when removed from reader visibility, and is
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incremented once per grace period subsequently -- and is freed
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after passing through (RCU_TORTURE_PIPE_LEN-2) grace periods.
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The output displayed above was taken from a correctly working
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RCU. If you want to see what it looks like when broken, break
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it yourself. ;-)
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o "Reader Batch": Another histogram of "ages" of structures seen
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by readers, but in terms of counter flips (or batches) rather
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than in terms of grace periods. The legal number of non-zero
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entries is again two. The reason for this separate view is that
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it is sometimes easier to get the third entry to show up in the
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"Reader Batch" list than in the "Reader Pipe" list.
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o "Free-Block Circulation": Shows the number of torture structures
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that have reached a given point in the pipeline. The first element
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should closely correspond to the number of structures allocated,
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the second to the number that have been removed from reader view,
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and all but the last remaining to the corresponding number of
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passes through a grace period. The last entry should be zero,
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as it is only incremented if a torture structure's counter
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somehow gets incremented farther than it should.
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Different implementations of RCU can provide implementation-specific
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additional information. For example, Tree SRCU provides the following
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additional line:
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srcud-torture: Tree SRCU per-CPU(idx=0): 0(35,-21) 1(-4,24) 2(1,1) 3(-26,20) 4(28,-47) 5(-9,4) 6(-10,14) 7(-14,11) T(1,6)
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This line shows the per-CPU counter state, in this case for Tree SRCU
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using a dynamically allocated srcu_struct (hence "srcud-" rather than
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"srcu-"). The numbers in parentheses are the values of the "old" and
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"current" counters for the corresponding CPU. The "idx" value maps the
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"old" and "current" values to the underlying array, and is useful for
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debugging. The final "T" entry contains the totals of the counters.
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USAGE
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The following script may be used to torture RCU:
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#!/bin/sh
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modprobe rcutorture
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sleep 3600
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rmmod rcutorture
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dmesg | grep torture:
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The output can be manually inspected for the error flag of "!!!".
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One could of course create a more elaborate script that automatically
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checked for such errors. The "rmmod" command forces a "SUCCESS",
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"FAILURE", or "RCU_HOTPLUG" indication to be printk()ed. The first
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two are self-explanatory, while the last indicates that while there
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were no RCU failures, CPU-hotplug problems were detected.
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However, the tools/testing/selftests/rcutorture/bin/kvm.sh script
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provides better automation, including automatic failure analysis.
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It assumes a qemu/kvm-enabled platform, and runs guest OSes out of initrd.
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See tools/testing/selftests/rcutorture/doc/initrd.txt for instructions
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on setting up such an initrd.
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