diff options
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/Design/Data-Structures/Data-Structures.rst | 2 | ||||
| -rw-r--r-- | Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst | 2 | ||||
| -rw-r--r-- | Documentation/RCU/Design/Requirements/Requirements.rst | 36 | ||||
| -rw-r--r-- | Documentation/RCU/arrayRCU.rst | 4 | ||||
| -rw-r--r-- | Documentation/RCU/checklist.rst | 9 | ||||
| -rw-r--r-- | Documentation/RCU/rcu.rst | 13 | ||||
| -rw-r--r-- | Documentation/RCU/rculist_nulls.rst | 2 | ||||
| -rw-r--r-- | Documentation/RCU/stallwarn.rst | 20 | ||||
| -rw-r--r-- | Documentation/RCU/whatisRCU.rst | 18 |
9 files changed, 77 insertions, 29 deletions
diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.rst b/Documentation/RCU/Design/Data-Structures/Data-Structures.rst index f4efd6897b09..b34990c7c377 100644 --- a/Documentation/RCU/Design/Data-Structures/Data-Structures.rst +++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.rst @@ -973,7 +973,7 @@ The ``->dynticks`` field counts the corresponding CPU's transitions to and from either dyntick-idle or user mode, so that this counter has an even value when the CPU is in dyntick-idle mode or user mode and an odd value otherwise. The transitions to/from user mode need to be counted -for user mode adaptive-ticks support (see timers/NO_HZ.txt). +for user mode adaptive-ticks support (see Documentation/timers/no_hz.rst). The ``->rcu_need_heavy_qs`` field is used to record the fact that the RCU core code would really like to see a quiescent state from the diff --git a/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst b/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst index 6f89cf1e567d..c9c957c85bac 100644 --- a/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst +++ b/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst @@ -406,7 +406,7 @@ In earlier implementations, the task requesting the expedited grace period also drove it to completion. This straightforward approach had the disadvantage of needing to account for POSIX signals sent to user tasks, so more recent implemementations use the Linux kernel's -`workqueues <https://www.kernel.org/doc/Documentation/core-api/workqueue.rst>`__. +workqueues (see Documentation/core-api/workqueue.rst). The requesting task still does counter snapshotting and funnel-lock processing, but the task reaching the top of the funnel lock does a diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst index 45278e2974c0..04ed8bf27a0e 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.rst +++ b/Documentation/RCU/Design/Requirements/Requirements.rst @@ -370,8 +370,8 @@ pointer fetched by rcu_dereference() may not be used outside of the outermost RCU read-side critical section containing that rcu_dereference(), unless protection of the corresponding data element has been passed from RCU to some other synchronization -mechanism, most commonly locking or `reference -counting <https://www.kernel.org/doc/Documentation/RCU/rcuref.txt>`__. +mechanism, most commonly locking or reference counting +(see ../../rcuref.rst). .. |high-quality implementation of C11 memory_order_consume [PDF]| replace:: high-quality implementation of C11 ``memory_order_consume`` [PDF] .. _high-quality implementation of C11 memory_order_consume [PDF]: http://www.rdrop.com/users/paulmck/RCU/consume.2015.07.13a.pdf @@ -2654,6 +2654,38 @@ synchronize_rcu(), and rcu_barrier(), respectively. In three APIs are therefore implemented by separate functions that check for voluntary context switches. +Tasks Rude RCU +~~~~~~~~~~~~~~ + +Some forms of tracing need to wait for all preemption-disabled regions +of code running on any online CPU, including those executed when RCU is +not watching. This means that synchronize_rcu() is insufficient, and +Tasks Rude RCU must be used instead. This flavor of RCU does its work by +forcing a workqueue to be scheduled on each online CPU, hence the "Rude" +moniker. And this operation is considered to be quite rude by real-time +workloads that don't want their ``nohz_full`` CPUs receiving IPIs and +by battery-powered systems that don't want their idle CPUs to be awakened. + +The tasks-rude-RCU API is also reader-marking-free and thus quite compact, +consisting of call_rcu_tasks_rude(), synchronize_rcu_tasks_rude(), +and rcu_barrier_tasks_rude(). + +Tasks Trace RCU +~~~~~~~~~~~~~~~ + +Some forms of tracing need to sleep in readers, but cannot tolerate +SRCU's read-side overhead, which includes a full memory barrier in both +srcu_read_lock() and srcu_read_unlock(). This need is handled by a +Tasks Trace RCU that uses scheduler locking and IPIs to synchronize with +readers. Real-time systems that cannot tolerate IPIs may build their +kernels with ``CONFIG_TASKS_TRACE_RCU_READ_MB=y``, which avoids the IPIs at +the expense of adding full memory barriers to the read-side primitives. + +The tasks-trace-RCU API is also reasonably compact, +consisting of rcu_read_lock_trace(), rcu_read_unlock_trace(), +rcu_read_lock_trace_held(), call_rcu_tasks_trace(), +synchronize_rcu_tasks_trace(), and rcu_barrier_tasks_trace(). + Possible Future Changes ----------------------- diff --git a/Documentation/RCU/arrayRCU.rst b/Documentation/RCU/arrayRCU.rst index 4051ea3871ef..a5f2ff8fc54c 100644 --- a/Documentation/RCU/arrayRCU.rst +++ b/Documentation/RCU/arrayRCU.rst @@ -33,8 +33,8 @@ Situation 1: Hash Tables Hash tables are often implemented as an array, where each array entry has a linked-list hash chain. Each hash chain can be protected by RCU -as described in the listRCU.txt document. This approach also applies -to other array-of-list situations, such as radix trees. +as described in listRCU.rst. This approach also applies to other +array-of-list situations, such as radix trees. .. _static_arrays: diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst index f4545b7c9a63..42cc5d891bd2 100644 --- a/Documentation/RCU/checklist.rst +++ b/Documentation/RCU/checklist.rst @@ -140,8 +140,7 @@ over a rather long period of time, but improvements are always welcome! prevents destructive compiler optimizations. However, with a bit of devious creativity, it is possible to mishandle the return value from rcu_dereference(). - Please see rcu_dereference.txt in this directory for - more information. + Please see rcu_dereference.rst for more information. The rcu_dereference() primitive is used by the various "_rcu()" list-traversal primitives, such @@ -151,7 +150,7 @@ over a rather long period of time, but improvements are always welcome! primitives. This is particularly useful in code that is common to readers and updaters. However, lockdep will complain if you access rcu_dereference() outside - of an RCU read-side critical section. See lockdep.txt + of an RCU read-side critical section. See lockdep.rst to learn what to do about this. Of course, neither rcu_dereference() nor the "_rcu()" @@ -323,7 +322,7 @@ over a rather long period of time, but improvements are always welcome! primitives when the update-side lock is held is that doing so can be quite helpful in reducing code bloat when common code is shared between readers and updaters. Additional primitives - are provided for this case, as discussed in lockdep.txt. + are provided for this case, as discussed in lockdep.rst. One exception to this rule is when data is only ever added to the linked data structure, and is never removed during any @@ -480,4 +479,4 @@ over a rather long period of time, but improvements are always welcome! both rcu_barrier() and synchronize_rcu(), if necessary, using something like workqueues to to execute them concurrently. - See rcubarrier.txt for more information. + See rcubarrier.rst for more information. diff --git a/Documentation/RCU/rcu.rst b/Documentation/RCU/rcu.rst index 0e03c6ef3147..3cfe01ba9a49 100644 --- a/Documentation/RCU/rcu.rst +++ b/Documentation/RCU/rcu.rst @@ -10,9 +10,8 @@ A "grace period" must elapse between the two parts, and this grace period must be long enough that any readers accessing the item being deleted have since dropped their references. For example, an RCU-protected deletion from a linked list would first remove the item from the list, wait for -a grace period to elapse, then free the element. See the -:ref:`Documentation/RCU/listRCU.rst <list_rcu_doc>` for more information on -using RCU with linked lists. +a grace period to elapse, then free the element. See listRCU.rst for more +information on using RCU with linked lists. Frequently Asked Questions -------------------------- @@ -50,7 +49,7 @@ Frequently Asked Questions - If I am running on a uniprocessor kernel, which can only do one thing at a time, why should I wait for a grace period? - See :ref:`Documentation/RCU/UP.rst <up_doc>` for more information. + See UP.rst for more information. - How can I see where RCU is currently used in the Linux kernel? @@ -64,13 +63,13 @@ Frequently Asked Questions - What guidelines should I follow when writing code that uses RCU? - See the checklist.txt file in this directory. + See checklist.rst. - Why the name "RCU"? "RCU" stands for "read-copy update". - :ref:`Documentation/RCU/listRCU.rst <list_rcu_doc>` has more information on where - this name came from, search for "read-copy update" to find it. + listRCU.rst has more information on where this name came from, search + for "read-copy update" to find it. - I hear that RCU is patented? What is with that? diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst index a9fc774bc400..ca4692775ad4 100644 --- a/Documentation/RCU/rculist_nulls.rst +++ b/Documentation/RCU/rculist_nulls.rst @@ -8,7 +8,7 @@ This section describes how to use hlist_nulls to protect read-mostly linked lists and objects using SLAB_TYPESAFE_BY_RCU allocations. -Please read the basics in Documentation/RCU/listRCU.rst +Please read the basics in listRCU.rst. Using 'nulls' ============= diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst index 78404625bad2..794837eb519b 100644 --- a/Documentation/RCU/stallwarn.rst +++ b/Documentation/RCU/stallwarn.rst @@ -162,6 +162,26 @@ CONFIG_RCU_CPU_STALL_TIMEOUT Stall-warning messages may be enabled and disabled completely via /sys/module/rcupdate/parameters/rcu_cpu_stall_suppress. +CONFIG_RCU_EXP_CPU_STALL_TIMEOUT +-------------------------------- + + Same as the CONFIG_RCU_CPU_STALL_TIMEOUT parameter but only for + the expedited grace period. This parameter defines the period + of time that RCU will wait from the beginning of an expedited + grace period until it issues an RCU CPU stall warning. This time + period is normally 20 milliseconds on Android devices. A zero + value causes the CONFIG_RCU_CPU_STALL_TIMEOUT value to be used, + after conversion to milliseconds. + + This configuration parameter may be changed at runtime via the + /sys/module/rcupdate/parameters/rcu_exp_cpu_stall_timeout, however + this parameter is checked only at the beginning of a cycle. If you + are in a current stall cycle, setting it to a new value will change + the timeout for the -next- stall. + + Stall-warning messages may be enabled and disabled completely via + /sys/module/rcupdate/parameters/rcu_cpu_stall_suppress. + RCU_STALL_DELAY_DELTA --------------------- diff --git a/Documentation/RCU/whatisRCU.rst b/Documentation/RCU/whatisRCU.rst index c34d2212eaca..77ea260efd12 100644 --- a/Documentation/RCU/whatisRCU.rst +++ b/Documentation/RCU/whatisRCU.rst @@ -224,7 +224,7 @@ synchronize_rcu() be delayed. This property results in system resilience in face of denial-of-service attacks. Code using call_rcu() should limit update rate in order to gain this same sort of resilience. See - checklist.txt for some approaches to limiting the update rate. + checklist.rst for some approaches to limiting the update rate. rcu_assign_pointer() ^^^^^^^^^^^^^^^^^^^^ @@ -318,7 +318,7 @@ rcu_dereference() must prohibit. The rcu_dereference_protected() variant takes a lockdep expression to indicate which locks must be acquired by the caller. If the indicated protection is not provided, - a lockdep splat is emitted. See Documentation/RCU/Design/Requirements/Requirements.rst + a lockdep splat is emitted. See Design/Requirements/Requirements.rst and the API's code comments for more details and example usage. .. [2] If the list_for_each_entry_rcu() instance might be used by @@ -399,8 +399,7 @@ for specialized uses, but are relatively uncommon. This section shows a simple use of the core RCU API to protect a global pointer to a dynamically allocated structure. More-typical -uses of RCU may be found in :ref:`listRCU.rst <list_rcu_doc>`, -:ref:`arrayRCU.rst <array_rcu_doc>`, and :ref:`NMI-RCU.rst <NMI_rcu_doc>`. +uses of RCU may be found in listRCU.rst, arrayRCU.rst, and NMI-RCU.rst. :: struct foo { @@ -482,10 +481,9 @@ So, to sum up: RCU read-side critical sections that might be referencing that data item. -See checklist.txt for additional rules to follow when using RCU. -And again, more-typical uses of RCU may be found in :ref:`listRCU.rst -<list_rcu_doc>`, :ref:`arrayRCU.rst <array_rcu_doc>`, and :ref:`NMI-RCU.rst -<NMI_rcu_doc>`. +See checklist.rst for additional rules to follow when using RCU. +And again, more-typical uses of RCU may be found in listRCU.rst, +arrayRCU.rst, and NMI-RCU.rst. .. _4_whatisRCU: @@ -579,7 +577,7 @@ to avoid having to write your own callback:: kfree_rcu(old_fp, rcu); -Again, see checklist.txt for additional rules governing the use of RCU. +Again, see checklist.rst for additional rules governing the use of RCU. .. _5_whatisRCU: @@ -663,7 +661,7 @@ been able to write-acquire the lock otherwise. The smp_mb__after_spinlock() promotes synchronize_rcu() to a full memory barrier in compliance with the "Memory-Barrier Guarantees" listed in: - Documentation/RCU/Design/Requirements/Requirements.rst + Design/Requirements/Requirements.rst It is possible to nest rcu_read_lock(), since reader-writer locks may be recursively acquired. Note also that rcu_read_lock() is immune |