diff options
Diffstat (limited to 'Documentation/RCU/Design')
3 files changed, 36 insertions, 4 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 ----------------------- |