diff options
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/Design/Requirements/Requirements.rst | 18 | ||||
| -rw-r--r-- | Documentation/RCU/stallwarn.rst | 23 |
2 files changed, 40 insertions, 1 deletions
diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst index 42a81e30619e..0da9133fa13a 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.rst +++ b/Documentation/RCU/Design/Requirements/Requirements.rst @@ -2598,6 +2598,24 @@ also includes DEFINE_SRCU(), DEFINE_STATIC_SRCU(), and init_srcu_struct() APIs for defining and initializing ``srcu_struct`` structures. +More recently, the SRCU API has added polling interfaces: + +#. start_poll_synchronize_srcu() returns a cookie identifying + the completion of a future SRCU grace period and ensures + that this grace period will be started. +#. poll_state_synchronize_srcu() returns ``true`` iff the + specified cookie corresponds to an already-completed + SRCU grace period. +#. get_state_synchronize_srcu() returns a cookie just like + start_poll_synchronize_srcu() does, but differs in that + it does nothing to ensure that any future SRCU grace period + will be started. + +These functions are used to avoid unnecessary SRCU grace periods in +certain types of buffer-cache algorithms having multi-stage age-out +mechanisms. The idea is that by the time the block has aged completely +from the cache, an SRCU grace period will be very likely to have elapsed. + Tasks RCU ~~~~~~~~~ diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst index e97d1b4876ef..7148e9be08c3 100644 --- a/Documentation/RCU/stallwarn.rst +++ b/Documentation/RCU/stallwarn.rst @@ -92,7 +92,9 @@ warnings: buggy timer hardware through bugs in the interrupt or exception path (whether hardware, firmware, or software) through bugs in Linux's timer subsystem through bugs in the scheduler, and, - yes, even including bugs in RCU itself. + yes, even including bugs in RCU itself. It can also result in + the ``rcu_.*timer wakeup didn't happen for`` console-log message, + which will include additional debugging information. - A bug in the RCU implementation. @@ -292,6 +294,25 @@ kthread is waiting for a short timeout, the "state" precedes value of the task_struct ->state field, and the "cpu" indicates that the grace-period kthread last ran on CPU 5. +If the relevant grace-period kthread does not wake from FQS wait in a +reasonable time, then the following additional line is printed:: + + kthread timer wakeup didn't happen for 23804 jiffies! g7076 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 + +The "23804" indicates that kthread's timer expired more than 23 thousand +jiffies ago. The rest of the line has meaning similar to the kthread +starvation case. + +Additionally, the following line is printed:: + + Possible timer handling issue on cpu=4 timer-softirq=11142 + +Here "cpu" indicates that the grace-period kthread last ran on CPU 4, +where it queued the fqs timer. The number following the "timer-softirq" +is the current ``TIMER_SOFTIRQ`` count on cpu 4. If this value does not +change on successive RCU CPU stall warnings, there is further reason to +suspect a timer problem. + Multiple Warnings From One Stall ================================ |