diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/RCU/Design/Requirements/Requirements.rst | 18 | ||||
| -rw-r--r-- | Documentation/RCU/stallwarn.rst | 23 | ||||
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 33 |
3 files changed, 73 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 ================================ diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index b5baa8a54df0..b1d6cd58a04c 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4092,6 +4092,10 @@ value, meaning that RCU_SOFTIRQ is used by default. Specify rcutree.use_softirq=0 to use rcuc kthreads. + But note that CONFIG_PREEMPT_RT=y kernels disable + this kernel boot parameter, forcibly setting it + to zero. + rcutree.rcu_fanout_exact= [KNL] Disable autobalancing of the rcu_node combining tree. This is used by rcutorture, and might @@ -4332,6 +4336,14 @@ stress RCU, they don't participate in the actual test, hence the "fake". + rcutorture.nocbs_nthreads= [KNL] + Set number of RCU callback-offload togglers. + Zero (the default) disables toggling. + + rcutorture.nocbs_toggle= [KNL] + Set the delay in milliseconds between successive + callback-offload toggling attempts. + rcutorture.nreaders= [KNL] Set number of RCU readers. The value -1 selects N-1, where N is the number of CPUs. A value @@ -4464,6 +4476,13 @@ only normal grace-period primitives. No effect on CONFIG_TINY_RCU kernels. + But note that CONFIG_PREEMPT_RT=y kernels enables + this kernel boot parameter, forcibly setting + it to the value one, that is, converting any + post-boot attempt at an expedited RCU grace + period to instead use normal non-expedited + grace-period processing. + rcupdate.rcu_task_ipi_delay= [KNL] Set time in jiffies during which RCU tasks will avoid sending IPIs, starting with the beginning @@ -4551,6 +4570,12 @@ refscale.verbose= [KNL] Enable additional printk() statements. + refscale.verbose_batched= [KNL] + Batch the additional printk() statements. If zero + (the default) or negative, print everything. Otherwise, + print every Nth verbose statement, where N is the value + specified. + relax_domain_level= [KNL, SMP] Set scheduler's default relax_domain_level. See Documentation/admin-guide/cgroup-v1/cpusets.rst. @@ -5325,6 +5350,14 @@ are running concurrently, especially on systems with rotating-rust storage. + torture.verbose_sleep_frequency= [KNL] + Specifies how many verbose printk()s should be + emitted between each sleep. The default of zero + disables verbose-printk() sleeping. + + torture.verbose_sleep_duration= [KNL] + Duration of each verbose-printk() sleep in jiffies. + tp720= [HW,PS2] tpm_suspend_pcr=[HW,TPM] |