Documentation/locking/locktorture.txt

   1 Kernel Lock Torture Test Operation
   2
   3 CONFIG_LOCK_TORTURE_TEST
   4
   5 The CONFIG LOCK_TORTURE_TEST config option provides a kernel module
   6 that runs torture tests on core kernel locking primitives. The kernel
   7 module, 'locktorture', may be built after the fact on the running
   8 kernel to be tested, if desired. The tests periodically output status
   9 messages via printk(), which can be examined via the dmesg (perhaps
  10 grepping for "torture").  The test is started when the module is loaded,
  11 and stops when the module is unloaded. This program is based on how RCU
  12 is tortured, via rcutorture.
  13
  14 This torture test consists of creating a number of kernel threads which
  15 acquire the lock and hold it for specific amount of time, thus simulating
  16 different critical region behaviors. The amount of contention on the lock
  17 can be simulated by either enlarging this critical region hold time and/or
  18 creating more kthreads.
  19
  20
  21 MODULE PARAMETERS
  22
  23 This module has the following parameters:
  24
  25
  26             ** Locktorture-specific **
  27
  28 nwriters_stress   Number of kernel threads that will stress exclusive lock
  29                   ownership (writers). The default value is twice the number
  30                   of online CPUs.
  31
  32 nreaders_stress   Number of kernel threads that will stress shared lock
  33                   ownership (readers). The default is the same amount of writer
  34                   locks. If the user did not specify nwriters_stress, then
  35                   both readers and writers be the amount of online CPUs.
  36
  37 torture_type      Type of lock to torture. By default, only spinlocks will
  38                   be tortured. This module can torture the following locks,
  39                   with string values as follows:
  40
  41                      o "lock_busted": Simulates a buggy lock implementation.
  42
  43                      o "spin_lock": spin_lock() and spin_unlock() pairs.
  44
  45                      o "spin_lock_irq": spin_lock_irq() and spin_unlock_irq()
  46                                         pairs.
  47
  48                      o "rw_lock": read/write lock() and unlock() rwlock pairs.
  49
  50                      o "rw_lock_irq": read/write lock_irq() and unlock_irq()
  51                                       rwlock pairs.
  52
  53                      o "mutex_lock": mutex_lock() and mutex_unlock() pairs.
  54
  55                      o "rwsem_lock": read/write down() and up() semaphore pairs.
  56
  57 torture_runnable  Start locktorture at boot time in the case where the
  58                   module is built into the kernel, otherwise wait for
  59                   torture_runnable to be set via sysfs before starting.
  60                   By default it will begin once the module is loaded.
  61
  62
  63             ** Torture-framework (RCU + locking) **
  64
  65 shutdown_secs     The number of seconds to run the test before terminating
  66                   the test and powering off the system.  The default is
  67                   zero, which disables test termination and system shutdown.
  68                   This capability is useful for automated testing.
  69
  70 onoff_interval    The number of seconds between each attempt to execute a
  71                   randomly selected CPU-hotplug operation.  Defaults
  72                   to zero, which disables CPU hotplugging.  In
  73                   CONFIG_HOTPLUG_CPU=n kernels, locktorture will silently
  74                   refuse to do any CPU-hotplug operations regardless of
  75                   what value is specified for onoff_interval.
  76
  77 onoff_holdoff     The number of seconds to wait until starting CPU-hotplug
  78                   operations.  This would normally only be used when
  79                   locktorture was built into the kernel and started
  80                   automatically at boot time, in which case it is useful
  81                   in order to avoid confusing boot-time code with CPUs
  82                   coming and going. This parameter is only useful if
  83                   CONFIG_HOTPLUG_CPU is enabled.
  84
  85 stat_interval     Number of seconds between statistics-related printk()s.
  86                   By default, locktorture will report stats every 60 seconds.
  87                   Setting the interval to zero causes the statistics to
  88                   be printed -only- when the module is unloaded, and this
  89                   is the default.
  90
  91 stutter           The length of time to run the test before pausing for this
  92                   same period of time.  Defaults to "stutter=5", so as
  93                   to run and pause for (roughly) five-second intervals.
  94                   Specifying "stutter=0" causes the test to run continuously
  95                   without pausing, which is the old default behavior.
  96
  97 shuffle_interval  The number of seconds to keep the test threads affinitied
  98                   to a particular subset of the CPUs, defaults to 3 seconds.
  99                   Used in conjunction with test_no_idle_hz.
 100
 101 verbose           Enable verbose debugging printing, via printk(). Enabled
 102                   by default. This extra information is mostly related to
 103                   high-level errors and reports from the main 'torture'
 104                   framework.
 105
 106
 107 STATISTICS
 108
 109 Statistics are printed in the following format:
 110
 111 spin_lock-torture: Writes:  Total: 93746064  Max/Min: 0/0   Fail: 0
 112    (A)              (B)            (C)            (D)          (E)
 113
 114 (A): Lock type that is being tortured -- torture_type parameter.
 115
 116 (B): Number of writer lock acquisitions. If dealing with a read/write primitive
 117      a second "Reads" statistics line is printed.
 118
 119 (C): Number of times the lock was acquired.
 120
 121 (D): Min and max number of times threads failed to acquire the lock.
 122
 123 (E): true/false values if there were errors acquiring the lock. This should
 124      -only- be positive if there is a bug in the locking primitive's
 125      implementation. Otherwise a lock should never fail (i.e., spin_lock()).
 126      Of course, the same applies for (C), above. A dummy example of this is
 127      the "lock_busted" type.
 128
 129 USAGE
 130
 131 The following script may be used to torture locks:
 132
 133         #!/bin/sh
 134
 135         modprobe locktorture
 136         sleep 3600
 137         rmmod locktorture
 138         dmesg | grep torture:
 139
 140 The output can be manually inspected for the error flag of "!!!".
 141 One could of course create a more elaborate script that automatically
 142 checked for such errors.  The "rmmod" command forces a "SUCCESS",
 143 "FAILURE", or "RCU_HOTPLUG" indication to be printk()ed.  The first
 144 two are self-explanatory, while the last indicates that while there
 145 were no locking failures, CPU-hotplug problems were detected.
 146
 147 Also see: Documentation/RCU/torture.txt